SIMS: A Hybrid Method for Rapid Conformational Analysis

Proteins are at the root of many biological functions, often performing complex tasks as the result of large changes in their structure. Describing the exact details of these conformational changes, however, remains a central challenge for computational biology due the enormous computational requirements of the problem. This has engendered the development of a rich variety of useful methods designed to answer specific questions at different levels of spatial, temporal, and energetic resolution. These methods fall largely into two classes: physically accurate, but computationally demanding methods and fast, approximate methods. We introduce here a new hybrid modeling tool, the Structured Intuitive Move Selector (SIMS), designed to bridge the divide between these two classes, while allowing the benefits of both to be seamlessly integrated into a single framework. This is achieved by applying a modern motion planning algorithm, borrowed from the field of robotics, in tandem with a well-established protein modeling library. SIMS can combine precise energy calculations with approximate or specialized conformational sampling routines to produce rapid, yet accurate, analysis of the large-scale conformational variability of protein systems. Several key advancements are shown, including the abstract use of generically defined moves (conformational sampling methods) and an expansive probabilistic conformational exploration. We present three example problems that SIMS is applied to and demonstrate a rapid solution for each. These include the automatic determination of ﾑﾑactiveﾒﾒ residues for the hinge-based system Cyanovirin-N, exploring conformational changes involving long-range coordinated motion between non-sequential residues in Ribose- Binding Protein, and the rapid discovery of a transient conformational state of Maltose-Binding Protein, previously only determined by Molecular Dynamics. For all cases we provide energetic validations using well-established energy fields, demonstrating this framework as a fast and accurate tool for the analysis of a wide range of protein flexibility problems

Multicolor plate reader fluorescence calibration

This is a pre-copyedited, author-produced version of an article accepted for publication in Synthetic Biology following peer review. The version of record Jacob Beal, Cheryl A Telmer, Alejandro Vignoni, Yadira Boada, Geoff S Baldwin, Liam Hallett, Taeyang Lee, Vinoo Selvarajah, Sonja Billerbeck, Bradley Brown, Guo-nan Cai, Liang Cai, Edward Eisenstein, Daisuke Kiga, David Ross, Nina Alperovich, Noah Sprent, Jaclyn Thompson, Eric M Young, Drew Endy, Traci Haddock-Angelli, Multicolor plate reader fluorescence calibration, Synthetic Biology, Volume 7, Issue 1, 2022, ysac010, https://doi.org/10.1093/synbio/ysac010, is available online at: https://doi.org/10.1093/synbio/ysac010.[EN] Plate readers are commonly used to measure cell growth and fluorescence, yet the utility and reproducibility of plate reader data is limited by the fact that it is typically reported in arbitrary or relative units. We have previously established a robust serial dilution protocol for calibration of plate reader measurements of absorbance to estimated bacterial cell count and for green fluorescence from proteins expressed in bacterial cells to molecules of equivalent fluorescein. We now extend these protocols to calibration of red fluorescence to the sulforhodamine-101 fluorescent dye and blue fluorescence to Cascade Blue. Evaluating calibration efficacy via an interlaboratory study, we find that these calibrants do indeed provide comparable precision to the prior calibrants and that they enable effective cross-laboratory comparison of measurements of red and blue fluorescence from proteins expressed in bacterial cells.This work was supported in part by the following funding sources: J.B. was supported by Air Force Research Laboratory (AFRL) and DARPA contract FA8750-17-C-0184. N.S. was supported by funding from the BBSRC under award BB/M011178/1. G.B., L.H., and T.L. were supported by the EPSRC under award EP/R034915/1 and EP/S022856/1. G.C. and L.C. were supported by funds from YF Capital and the National Top Talent Undergraduate Training Program, China. A.V. and Y.B. were funded by Grant MINECO/AEI, EU DPI2017-82896-C2-1-R and MCIN/AEI/10.13039/501100011033 grant number PID2020117271RB-C21. Y.B. was supported by Secretaria de Educaci ' on Superior, Ciencia, Tecnologia e Innovacion-Ecuador (Scholarship Convocatoria Abierta 2011). D.K. was supported by JST, CREST Grant Number JPMJCR21N4, Japan. E.Y. was supported by the National Science Foundation under Grant No. 1939860. J.T. was supported by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA) under Finding Engineering Linked Indicators (FELIX) program contract N66001-18-C-4507. This document does not contain technology or technical data controlled under either the U.S. International Traffic in Arms Regulations or the U.S. Export Administration Regulations. Views, opinions, and/or findings expressed are those of the author(s) and should not be interpreted as representing the official views or policies of the Department of Defense or the U.S. Government.Beal, J.; Telmer, CA.; Vignoni, A.; Boada-Acosta, YF.; Baldwin, GS.; Hallett, L.; Lee, T.... (2022). Multicolor plate reader fluorescence calibration. Synthetic Biology. 7(1):1-9. https://doi.org/10.1093/synbio/ysac010197

Multicolor plate reader fluorescence calibration

Plate readers are commonly used to measure cell growth and fluorescence, yet the utility and reproducibility of plate reader data is limited by the fact that it is typically reported in arbitrary or relative units. We have previously established a robust serial dilution protocol for calibration of plate reader measurements of absorbance to estimated bacterial cell count and for green fluorescence from proteins expressed in bacterial cells to molecules of equivalent fluorescein. We now extend these protocols to calibration of red fluorescence to the sulforhodamine-101 fluorescent dye and blue fluorescence to Cascade Blue. Evaluating calibration efficacy via an interlaboratory study, we find that these calibrants do indeed provide comparable precision to the prior calibrants and that they enable effective cross-laboratory comparison of measurements of red and blue fluorescence from proteins expressed in bacterial cells

Mutations in maltose-binding protein that alter affinity and solubility properties

Maltose-binding protein (MBP) from Escherichia coli has been shown to be a good substrate for protein engineering leading to altered binding (Marvin and Hellinga, Proc Natl Acad Sci U S A 98:4955–4960, 2001a) and increased affinity (Marvin and Hellinga, Nat Struct Biol 8:795–798, 2001b; Telmer and Shilton, J Biol Chem 278:34555–34567, 2003). It is also used in recombinant protein expression as both an affinity tag and a solubility tag. We isolated mutations in MBP that enhance binding to maltodextrins 1.3 to 15-fold, using random mutagenesis followed by screening for enhanced yield in a microplate-based affinity purification. We tested the mutations for their ability to enhance the yield of a fusion protein that binds poorly to immobilized amylose and their ability to enhance the solubility of one or more aggregation-prone recombinant proteins. We also measured dissociation constants of the mutant MBPs that retain the solubility-enhancing properties of MBP and combined two of the mutations to produce an MBP with a dissociation constant 10-fold tighter than wild-type MBP. Some of the mutations we obtained can be rationalized based on the previous work, while others indicate new ways in which the function of MBP can be modified

Structure of an Engineered β-Lactamase Maltose Binding Protein Fusion Protein: Insights into Heterotropic Allosteric Regulation

Engineering novel allostery into existing proteins is a challenging endeavor to obtain novel sensors, therapeutic proteins, or modulate metabolic and cellular processes. The RG13 protein achieves such allostery by inserting a circularly permuted TEM-1 β-lactamase gene into the maltose binding protein (MBP). RG13 is positively regulated by maltose yet is, serendipitously, inhibited by Zn2+ at low µM concentration. To probe the structure and allostery of RG13, we crystallized RG13 in the presence of mM Zn2+ concentration and determined its structure. The structure reveals that the MBP and TEM-1 domains are in close proximity connected via two linkers and a zinc ion bridging both domains. By bridging both TEM-1 and MBP, Zn2+ acts to “twist tie” the linkers thereby partially dislodging a linker between the two domains from its original catalytically productive position in TEM-1. This linker 1 contains residues normally part of the TEM-1 active site including the critical β3 and β4 strands important for activity. Mutagenesis of residues comprising the crystallographically observed Zn2+ site only slightly affected Zn2+ inhibition 2- to 4-fold. Combined with previous mutagenesis results we therefore hypothesize the presence of two or more inter-domain mutually exclusive inhibitory Zn2+ sites. Mutagenesis and molecular modeling of an intact TEM-1 domain near MBP within the RG13 framework indicated a close surface proximity of the two domains with maltose switching being critically dependent on MBP linker anchoring residues and linker length. Structural analysis indicated that the linker attachment sites on MBP are at a site that, upon maltose binding, harbors both the largest local Cα distance changes and displays surface curvature changes, from concave to relatively flat becoming thus less sterically intrusive. Maltose activation and zinc inhibition of RG13 are hypothesized to have opposite effects on productive relaxation of the TEM-1 β3 linker region via steric and/or linker juxtapositioning mechanisms

Accessing a Hidden Conformation of the Maltose Binding Protein Using Accelerated Molecular Dynamics

Periplasmic binding proteins (PBPs) are a large family of molecular transporters that play a key role in nutrient uptake and chemotaxis in Gram-negative bacteria. All PBPs have characteristic two-domain architecture with a central interdomain ligand-binding cleft. Upon binding to their respective ligands, PBPs undergo a large conformational change that effectively closes the binding cleft. This conformational change is traditionally viewed as a ligand induced-fit process; however, the intrinsic dynamics of the protein may also be crucial for ligand recognition. Recent NMR paramagnetic relaxation enhancement (PRE) experiments have shown that the maltose binding protein (MBP) - a prototypical member of the PBP superfamily - exists in a rapidly exchanging (ns to µs regime) mixture comprising an open state (approx 95%), and a minor partially closed state (approx 5%). Here we describe accelerated MD simulations that provide a detailed picture of the transition between the open and partially closed states, and confirm the existence of a dynamical equilibrium between these two states in apo MBP. We find that a flexible part of the protein called the balancing interface motif (residues 175–184) is displaced during the transformation. Continuum electrostatic calculations indicate that the repacking of non-polar residues near the hinge region plays an important role in driving the conformational change. Oscillations between open and partially closed states create variations in the shape and size of the binding site. The study provides a detailed description of the conformational space available to ligand-free MBP, and has implications for understanding ligand recognition and allostery in related proteins

Losing Track of the Asset Markets: The Case of Housing and Stock

This paper revisits the relationships among macroeconomic variables and asset returns. Based on recent developments in econometrics, we categorize competing models of asset returns into different "Equivalence Predictive Power Classes" (EPPC). During the pre-crisis period (1975-2005), some models that emphasize imperfect capital markets outperform an AR(1) for the forecast of housing returns. After 2006, a model that includes both an external finance premium (EFP) and the TED spread "learns and adjusts" faster than competing models. Models that encompass GDP experience a significant decay in predictive power. We also demonstrate that a simulation-based approach is complementary to the EPPC methodology