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Foresight Update 21 - Table of Contents | Page1 | Page2 | Page3 | Page4 |
Concepts in Protein Engineering and Design, ed. Paul
Wrede and Gisbert Schneider, Walter de Gruyter & Co., 1994,
378 pgs, some color illustrations.
This volume provides an excellent survey of the state of the art
in protein engineering, covering topics ranging from protein
analysis to the use of neural network techniques in protein
sequence design. Taken as a whole, it offers a good picture both
of the achievements to date and of the challenges that remain. As
a bonus, the last chapter (by Nadrian Seeman, a speaker at the
second Foresight Conference) describes achievements in the
engineering of three-dimensional structures from nucleic acids.
Readers with a background in chemistry or molecular biology will
find this book a valuable introduction to biomolecular
engineering, which may prove to be a key step on the path to
advanced nanotechnologies. Its focus on achievable steps that are
on today's research agenda will suggest practical career moves
for those with their eyes on the road ahead.
-Eric Drexler
Foresight Update 21 - Table of Contents |
Prospects in Nanotechnology: Toward Molecular Manufacturing,
ed. Markus Krummenacker and James Lewis, Wiley, 1995, 297 pages,
hardcover. Proceedings of the First Foresight General Conference;
see announcement in this issue.
Experiment Zukunft: Die Nanotechnologische Revolution, by
K. Eric Drexler, Chris Peterson, with Gayle Pergamit, Addison
Wesley, 1995, 320 pages, hardcover. German edition of Unbounding the
Future.
Technotrends by Daniel Burrus, HarperBusiness, 1994,
paperback. Gives "24 technologies that will revolutionize
our lives," but does not get nanotechnology quite right.
Confuses the current ability to design and build molecules (e.g.
new enzymes) and the coming ability to design and build
molecularly-precise materials. Confuses micromechanics
(mechanics) with quantum structures (electronics). Author is
"one of the world's leading technology forecasters,"
and his basic point -- the importance of emerging technologies to
business -- is excellent. Let's educate him further.
Foresight Update 21 - Table of Contents |
Foresight is pleased
to announce the publication of Prospects in Nanotechnology:
Toward Molecular Manufacturing (John Wiley & Sons, Inc.,
1995). When we held our first conference for non-researchers we
weren't planning a proceedings book, but thanks to long hours of
hard work by coeditors (and Senior Associates) Markus
Krummenacker and James Lewis, many of the papers presented are
now available in one volume. Because Wiley is a technical
publisher, the papers selected are the more technical ones
presented, but all are accessible to the general reader.
From the back cover of the book:
A fascinating journey through the microscopic world of
nanotechnology and its macroscopic implications
Complex mechanical devices with feature sizes on the molecular
scale and with all the power of today's supercomputers; diamond
and other ultrastrong building materials-and all of this
accessible through low-cost automated molecular manufacturing.
We've all read about the vast potential of nanotechnology. Some
theorists have hailed it as the most important technological
breakthrough since steam power. But how far have we really come
to realizing any of that potential? And how have recent
developments in the field already begun to shape the world of the
twenty-first century?
Now this discussion-oriented book takes you to the front lines of
nanotechnology theory and practice to provide answers to these
and other questions. Featuring contributions from a number of
international top names in the field, it offers a provocative
look into a future shaped by nanotechnological applications and
also provides an overview of the enabling technologies that are
in current use in a variety of industries, and which will be
important in attaining this breakthrough technology.
Markus Krummenacker,
a former researcher at the Institute for Molecular Manufacturing,
now working with Nanothinc, a San Francisco-based company.
James Lewis, Ph.D.,
is a scientist at Bristol-Myers Squibb Pharmaceutical Research
Institute in Seattle. Dr. Lewis is author of more than forty
scientific research publications in biochemistry, virology, and
molecular biology.
Foreword by K. Eric Drexler
Index
To order.
Foresight Update 21 - Table of Contents |
Most Foresight conferences have been highly technical, but
those of you who attended the 1992 General Conference will recall
that it was specifically designed for those not engaged in
research, covering the topic of nanotechnology for the
non-technical participant.
There was some confusion at the meeting: the press-expecting a
research conference-did not know what to make of it, and the
background level of knowledge of the participants varied widely.
Still, many Foresight members enjoyed the event tremendously and
asked for more.
The annual Senior Associates Gathering, begun formally in 1994,
provides the value of the former General Conference with the
following improvements: (1) we do not look for press coverage; in
fact, the meeting is regarded as off-the-record, to encourage
freer discussion, and (2) the level of knowledge and commitment
of participants is kept high by drawing from the Senior
Associates groups of Foresight, IMM, and CCIT. This also keeps
the size of the group down to a level that enables a more
intense, interactive meeting. Participants are expected to have
read Engines of Creation or Unbounding the Future.
The 1995 Gathering will take place on November 11-12 in the Bay
Area. Those wishing to participate who are not already Senior
Associates can request a Senior Associate information package
from the Foresight office. Senior Associates make a five-year
pledge of $250, $500, or $1000 annually.
For a Senior Associate information package, contact Foresight
at tel 415-917-1122; fax 415-917-1123; or email office@foresight.org.
Foresight Update 21 - Table of Contents |
[Editor's Note: This page has been optimized for Netscape 2 and later. If you are using a browser, such as Netscape 1.1, that does not support the html tag for superscripts, please be aware that an number like "2x109" is meant to be scientific notation for "2 times ten raised to the 9th power," and that "e2" means "e squared," etc.]
Robertson, Dunlap, Brenner, Mintmire, and White at NRL
described simulations of atomically perfect fullerene gears. They
designed 5-8 sprocket gears with 290-464 atoms. A six-tooth gear
was extended with a fullerene shaft to simulate the shaft that
would conduct mechanical power in a complete machine. Simulations
of power transmission from one gear to another were done with a reactive
potential, so the simulation verified that the bonds in the
structure would withstand the forces applied. During one
simulation, one gear spun up the other from a standing start to
20 gigarev/sec in a quarter of a turn. In addition, the overall
binding energies of the gears were calculated. They were
uniformly found to be more stable (per atom) than C60.
[Novel Forms of Carbon II 283-288]
In experimental news on fullerene systems, Lüthi et al.
measured unusually low friction (a shear strength of 0.05 to 0.1
megapascal) between C60 islands and an NaCl substrate
using a scanning force microscope. They note that "These
results could find use in the field of nanotechnology; for
example, C60 islands could be developed into a
sled-type transport system on the nanometer scale." [Science
266: 1979-1981, 23Dec94]
In more general news on friction, Singer wrote a review article
on studies of friction at the level of molecular mechanics
simulations. Oddly, there is almost no overlap with Drexler's
analysis in Nanosystems. The investigations described are
all of much more dissipative systems than would be desirable for
mature nanotechnology. The dominant dissipation mechanism in
evidence is irreversible merging of potential wells (ideally
confined to erasure of bits, but occurring here whenever methyl
groups pass each other on a surface). At the level of accuracy
relevant in this paper, "Low friction, including zero
friction, can be achieved at low loads, with weak surface
interactions and with 'small' atoms at the interface." The
extensions suggested for current work are towards pushing the
length and time scales upwards to better predict current
macroscopic systems, rather than to optimize microscopic systems.
The analysis is interesting for contemporary lubrication systems,
and may be important for analysis of early protein machines, but
hopefully these mechanisms will be designed out of mature
nanomachines. [J.Vac.Sci.Tech.A 12(5) 2605-2616,
Sep/Oct 1994]
Foresight Update 21 - Table of Contents |
Friction is important once one has a means to move things at
all. One approach to supplying energy for movement is to use
chemical energy sources. An analysis paper by Magnasco provides a
general framework for calculating the properties of
"Molecular Combustion Motors." Magnasco describes
molecular motors with a potential energy surface on two
coordinates: the reaction coordinate for fuel burning, and the
mechanical movement coordinate. Given this potential surface,
this paper describes how to calculate fuel consumption rate,
speed of movement as a function of load, and so on. There is an
interesting analogy made for the losses due to thermally
activated slipping on the potential energy landscape. "It is
evident that thermal noise will allow the gears to slide over
each other, not unlike actual engine transmission coupling
through transmission fluid before the teeth actually lock."
[Phys. Rev. Let. 72: 2656-2659, 18Apr9 4]
In more concrete work on a specific motor system, a paper by
Spudich describes work on the myosin motor in biological systems.
He describes the current understanding of the chemical kinetics
of this molecule, how some structural features of the molecule
affect reaction rate, and where in the reaction cycle the rate
limiting effects appear. For nanotech applications the coupling
between chemical energy and mechanical energy will continue to be
useful, but some more precise mechanism to single-step the motor
will be necessary in order to use it for atomically precise
operations. Thermally activated ADP desorbtion won't be
sufficiently precise for that application. He also describes a
laser-trap system which allowed observation of single steps of
10-20nm, and forces of 7 pN.
Spudich also points out that "laser-trap technology allows
many types of measurements that could be applied to virtually any
protein. For example, the elasticity of a protein molecule can
now be measured directly, and conformational changes associated
with transitions between states are within reach of being
explored." This capability sounds promising; however, there
may be considerable duplication between this technique and AFM,
which probes similar ranges of parameters. [Nature 372:
515-518, 8Dec94]
Foresight Update 21 - Table of Contents |
Proteins offer us a great deal of synthetic flexibility today.
We have well-tested methods for building custom proteins, both
biologically based and chemically based. These methods, however,
let us select the primary structure of a protein: the sequence of
amino acid residues within it. In order to use a protein as part
of a structure, or to place groups within it in some pattern in
space in order to control a reaction or bind to some substrate,
we must control the secondary and tertiary structure of the
protein: how it folds and assembles itself in space. We must go
"from structure to sequence."
Steven Brenner and Alan Berry have written a program to help
systematically select amino acid sequences designed to fold in a
prespecified way. Their program relies primarily on the
statistics of the structures of known natural proteins. It takes
a desired structure as an input, which specifies which parts of
the amino acid sequence are in what types of secondary structures
(alpha-helices, beta sheets, and so on) and how much each residue
is exposed to the solvent. The program uses simulated annealing
to pick sequences of amino acids which match the conformational
preferences, the neighbor preferences, and the solvent
accessibilities of the protein database. Another bias-term in the
process selects for "diverse" sequences, those where
the overall frequencies of residues in the sequence match the
frequencies in the database. The justification for this
nonstructural term is that it biases the designed sequences
against designs that would fold in too many ways. One needs to
avoid designing proteins that fold in the way that one
wants...but fold even more stably in some other way. The
sequences that were designed were tested by computer analysis in
an independent program, and their predicted structures compared
with the intended structure. [Protein Science 3:
1871-1882, 1994]
There have been a number of experimental protein design papers
recently:
A group at Lausanne, Switzerland, assembled and demonstrated the
function of an ion channel built from 4 copies of a natural
peptide covalently linked to a 10 residue "template"
peptide. In this design the peptide bonds to NH2 side
chains of lysine residues in the template provide the structure
that is typically provided by protein folding in ordinary
proteins. The group was able to measure the conductances from
single channels. One somewhat disturbing note is that "Three
different channel states (called 01, 02 and 03) can be clearly
distinguished." The channel states seem to imply that
several active states are thermodynamically accessible, which
would be unfortunate if we wish to exploit stable, unique
structures for protein designs. [Protein Science 3:
1788-1805, 1994]
Munson et al. redesigned the 4-helix-bundle protein Rop.
They repacked the hydrophobic core, achieving better thermal
stability than in the original protein. The redesign was done by
examining packing effects in space-filling molecular models. The
protein consists of two copies of a 63-residue chain. Several
modified versions of this protein were designed, with 7 and 9
residues changed in two versions. The revised protein was
produced biologically. The 50% denaturing temperature was raised
from 74.6C to 87.2C and 95.4C in two variants. Energy
minimization of the modified proteins gave backbones which were
"superimposable on the wild-type backbone." This showed
that the energetics of the hydrophobic core were well explained
by space filling considerations. [Protein Science 3:
2015-2022, 1994]
Fezoui, Weaver, and Osterhout described how they designed a
38-residue peptide in 1990. Their peptide was designed to have a
simple, predictable tertiary structure. It consists of two
helices covalently linked by a hairpin turn. The two helices were
designed to have mutually stabilizing hydrophobic regions where
they touched. A noteworthy constraint on the design was avoiding
undesired aggregation between copies of the peptides. This set an
upper bound on how large the hydrophobic region of the
peptides could be. This is somewhat discouraging for designing
multi-peptide structures, since the desirable structures for
bonding the peptides together include hydrophobic regions, which
will tend to destabilize the individual peptides and tend to make
them form undesired aggregates before they are mixed to form the
desired ones. After the design of the hydrophobic regions in this
design, charged residues were selected to form salt bridges
between the two helices to further stabilize the structure. In
the last step of the design, 12 remaining residues were selected,
including a fluorescent donor and acceptor. These last residues
were constrained to be good helix formers. Three residues met
this contraint, so roughly 312 possibilities remain
for this design after all of the constraints are met.
The authors also describe the degree of structural success that
they had. "CD experiments indicate that the peptide is
approximately 60% helical at room temperature (89% of the
residues are in the helical regions of the peptide), suggesting
that the helices are slightly frayed and/or that the peptide is
in equilibrium with unfolded, nonhelical conformations." The
authors goals for further work in the field are consistent with
the requirements of nanotechnology in that they are looking for
more rigid structures. "...a major focus of the protein
design field must be upon how to achieve protein designs with
more rigid protein-like interiors." This is a requirement
even for improving the quality of feedback about designs:
"It is hoped that relatively simple notions of space filling
can be used to design molecules that will exhibit enough
structure to characterize by high-resolution techniques (NMR and
X-ray diffraction)." [Protein Science 4:
286-295, 1995]
In supramolecular chemistry, Jin and Wells have shown that
attractiveness is only about one residue deep, yet it is hard to
graft. They studied the affinities of a series of antibodies to a
series of mutated antigens and found that only a small number of
residues on the antigens account for the bulk of the binding
energy. They found that "...on average only 3-5 side chains
could account for more than 80% of the binding..." There are
x-ray studies to contrast these with, and they show far more
residues physically in contact, "14-21 residues on each
side." Jin and Wells were able to mutate as many as 16 neighboring
residues to alanine without lowering the affinity by more than a
factor of 10, while changing a single one of the 5 primary
residues "caused a 6- to >500-fold reduction in
affinity." While this appears to indicate that
intermolecular affinity should be comparatively easy to produce,
grafting the critical residues on to another antigen only worked
when it was homologous to the original antigen. [Protein
Science 3: 2351-2357, 1994]
Foresight Update 21 - Table of Contents |
Organic Chemistry
In classical organic chemistry, Nicolaou and co-workers have
synthesized Brevetoxin B. The molecule consists of 11 fused rings
(all of which are cyclic ethers) with 23 stereocenters. The
synthesis required 33 man-years by 25 graduate students and
postdoctoral fellows spread across 12 calendar years. There are
83 steps in the synthesis, with an average yield for each step of
91%, and an overall yield of 0.043%. "The synthetic strategy
was a convergent one, in which large parts of the molecule were
preassembled and then combined." [C&EN 32- 33,
30Jan95]
In another synthetic note, Lagow et al. synthesized
carbyne rods "with chain lengths in excess of 300 carbon
atoms." The longest chains were produced by alternately
condensing CF3 radicals from a C2F6
RF discharge and laser vaporized graphite on the walls of a glass
reactor. The rods are not particularly reactive. They were
dissolved in THF and toluene during the course of analysis.
Related model compounds could be crystallized and heated to 130C
before polymerizing. Unfortunately, attempts to separate some
related reaction mixtures on the types of columns (Al2O3)
used to separate fullerenes did not separate them, but rather
they reacted with the column. I wish them better luck in future
separation efforts. If we can separate 235U from 238U,
surely there must be some way to separate F3C(CC)150CF3
from F3C(CC)151CF3. Nonetheless,
it is encouraging to see that the rods used in the original rod
logic proposal are in fact quite stable at room temperature, even
without any solid matrix to prevent collisions. Useful mechanical
components may be available right down to the limit of chemically
plausible structures. [Science 267: 362-367,
20Jan95]
Jeffrey Soreff is a researcher at IBM with an interest in
nanotechnology.
Foresight Update 21 - Table of Contents | Page1 | Page2 | Page3 | Page4 |
From Foresight Update 21, originally
published 1 June 1995.
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