Functional Implications Of Disordered Terminal Regions Of Macrotyloma uniflorum Bowman-Birk Inhibitors: A Molecular Dynamics Study

Abstract

Bowman-Birk Inhibitors (BBI) - a class of serine protease inhibitors is of considerable interest due to their anti-inflammatory and anti-carcinogenic properties. Recent efforts have focused on understanding the structure and dynamics of these inhibitors, and the molecular mechanism behind its bioactive properties. BBI derived from Horsegram seeds is an interesting member of the class that exists as a number of isoforms that differ in length at the C- and N-terminal disordered regions. Interestingly, the length (or conversely, truncation) of the terminal regions affect whether the protein exists as a dimer or monomer. Here, we have investigated the mechanism of dimerization in Horsegram BBI. A recent study has proposed that the dimerization occur via a C-terminal hook that forms a salt bridge with the opposite monomer and is pivotal to the dimerization process. We have employed long computational simulation methods to predict the stability of the proposed C-terminal hook; we show that the terminal regions are highly disordered and the salt bridges are significantly solvent exposed. Further, using Hamiltonian replica exchange method, we have sought to obtain the conformational ensemble of the disordered terminal regions and have identified a conformational state that provides an interaction hot-spot that aids in the dimerization of HGI. Our analysis predicts an alternate model of dimerization that largely agrees with previous experimental studies and yet again, highlights the importance of intrinsically disordered region in tailoring the protein function.