Christopher N. Lam

Bio: Christopher N. Lam is an academic researcher from Oak Ridge National Laboratory. The author has contributed to research in topics: Globular protein & Micelle. The author has an hindex of 12, co-authored 24 publications receiving 450 citations. Previous affiliations of Christopher N. Lam include Rice University & Massachusetts Institute of Technology.

Phase transitions in concentrated solution self-assembly of globular protein–polymer block copolymers

Abstract: The phase behaviour of mCherry-b-PNIPAM (mChP) block copolymers with four different PNIPAM coil fractions is investigated in concentrated aqueous solution as a function of both concentration and temperature, demonstrating both order–order transitions (OOTs) and order–disorder transitions (ODTs) in globular protein–polymer block copolymers. Independent of coil volume fraction from 0.25 to 0.70, the temperature–concentration phase diagrams share several common features. At low concentrations, mCherry-b-PNIPAM forms a homogeneous disordered phase, and macrophase separation into an ordered conjugate-rich phase and a solvent-rich phase is observed at temperatures above the PNIPAM thermoresponsive transition temperature. mChP solutions are also observed to undergo a low-temperature ODT driven by increasing concentration. The order–disorder transition concentration (ODTC) behaviour of mChP is minimized for symmetric conjugates, suggesting that repulsive solvent-mediated protein–polymer interactions provide a driving force for self-assembly. Both coil fraction and solvent selectivity have large effects on the morphologies formed—disordered micelles, hexagonally packed cylinders, lamellae, and perforated lamellae are identified with the combination of small-angle X-ray scattering (SAXS), depolarized light scattering (DPLS), turbidimetry, and differential scanning calorimetry (DSC). An OOT is observed upon increasing temperature for three of the studied coil fractions at concentrations of 40–50 wt% due to changing solvent selectivity. SANS contrast-matching experiments show that water is weakly selective for PNIPAM at low temperatures and strongly selective for mCherry at high temperatures.

Phase Transitions in Concentrated Solution Self-Assembly of Globular Protein-Polymer Block Copolymers

Abstract: The phase behaviour of mCherry-b-PNIPAM (mChP) block copolymers with four different PNIPAM coil fractions is investigated in concentrated aqueous solution as a function of both concentration and temperature, demonstrating both order–order transitions (OOTs) and order–disorder transitions (ODTs) in globular protein–polymer block copolymers. Independent of coil volume fraction from 0.25 to 0.70, the temperature–concentration phase diagrams share several common features. At low concentrations, mCherry-b-PNIPAM forms a homogeneous disordered phase, and macrophase separation into an ordered conjugate-rich phase and a solvent-rich phase is observed at temperatures above the PNIPAM thermoresponsive transition temperature. mChP solutions are also observed to undergo a low-temperature ODT driven by increasing concentration. The order–disorder transition concentration (ODTC) behaviour of mChP is minimized for symmetric conjugates, suggesting that repulsive solvent-mediated protein–polymer interactions provide a driving force for self-assembly. Both coil fraction and solvent selectivity have large effects on the morphologies formed—disordered micelles, hexagonally packed cylinders, lamellae, and perforated lamellae are identified with the combination of small-angle X-ray scattering (SAXS), depolarized light scattering (DPLS), turbidimetry, and differential scanning calorimetry (DSC). An OOT is observed upon increasing temperature for three of the studied coil fractions at concentrations of 40–50 wt% due to changing solvent selectivity. SANS contrast-matching experiments show that water is weakly selective for PNIPAM at low temperatures and strongly selective for mCherry at high temperatures.

Fingerprinting Molecular Relaxation in Deformed Polymers

Abstract: Results from a new method of analyzing neutron-scattering data from polymer samples under deformation may challenge the prevailing ``tube model'' of polymer motion.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Protein Assembly: Versatile Approaches to Construct Highly Ordered Nanostructures

Abstract: Nature endows life with a wide variety of sophisticated, synergistic, and highly functional protein assemblies. Following Nature’s inspiration to assemble protein building blocks into exquisite nanostructures is emerging as a fascinating research field. Dictating protein assembly to obtain highly ordered nanostructures and sophisticated functions not only provides a powerful tool to understand the natural protein assembly process but also offers access to advanced biomaterials. Over the past couple of decades, the field of protein assembly has undergone unexpected and rapid developments, and various innovative strategies have been proposed. This Review outlines recent advances in the field of protein assembly and summarizes several strategies, including biotechnological strategies, chemical strategies, and combinations of these approaches, for manipulating proteins to self-assemble into desired nanostructures. The emergent applications of protein assemblies as versatile platforms to design a wide variety ...