This
Article describes a novel geometric methodology for analyzing
free energy and kinetics of assembly driven by short-range pair-potentials
in an implicit solvent and provides a proof-of-concept illustration
of its unique capabilities. An atlas is a labeled
partition of the assembly landscape into a roadmap of maximal, contiguous,
nearly-equipotential-energy conformational regions or macrostates,
together with their neighborhood relationships. The new methodology
decouples the roadmap generation from sampling and produces: (1) a
queryable atlas of local potential energy minima, their basin structure,
energy barriers, and neighboring basins; (2) paths between a specified
pair of basins, each path being a sequence of conformational regions
or macrostates below a desired energy threshold; and (3) approximations
of relative path lengths, basin volumes (configurational entropy),
and path probabilities. Results demonstrating the core algorithm’s
capabilities and high computational efficiency have been generated
by a resource-light, curated open source software implementation EASAL
(Efficient Atlasing and Search of Assembly Landscapes, 10.1145/3204472ACM Trans. Math. Softw.201844148; see software, Efficient Atlasing and Search of Assembly
Landscapes2016; video, Video
Illustrating the opensource software EASAL2016; and user guide, EASAL software user guide2016). Running on a laptop with Intel(R) Core(TM) i7-7700@3.60
GHz CPU with 16GB of RAM, EASAL atlases several hundred thousand conformational
regions or macrostates in minutes using a single compute core. Subsequent
path and basin computations each take seconds. A parallelized EASAL
version running on the same laptop with 4 cores gives a 3× speedup
for atlas generation. The core algorithm’s correctness, time
complexity, and efficiency–accuracy trade-offs are formally
guaranteed using modern distance geometry, geometric constraint systems
and combinatorial rigidity. The methodology further links the shape
of the input assembling units to a type of intuitive and queryable
bar-code of the output atlas, which in turn determine stable assembled
structures and kinetics. This succinct input–output relationship
facilitates reverse analysis and control toward design. A novel feature
that is crucial to both the high sampling efficiency and decoupling
of roadmap generation from sampling is a recently developed theory
of convex Cayley (distance-based) custom parametrizations specific
to assembly, as opposed to folding. Representing microstates with
macrostate-specific Cayley parameters, to generate microstate samples,
avoids gradient-descent search used by all prevailing methods. Further,
these parametrizations convexify conformational regions or macrostates.
This ratchets up sampling efficiency, significantly reducing number
of repeated and discarded samples. These features of the new stand-alone
methodology can also be used to complement the strengths of prevailing
methodologies including Molecular Dynamics, Monte Carlo, and Fast
Fourier Transform based methods.