DISSERTATION DEFENSE

Author : Hanin Omar

Advisor : Dr. Homayoun Valafar

Date : March 21, 2022

Time: 9:30 am

Place: Virtual Teams Link

Abstract

A complete understanding of the structure-function relationship of proteins requires an analysis of their dynamic behaviors in addition to the static structure. However, all current approaches to the study of dynamics in proteins have their shortcomings. A conceptually attractive and alternative approach simultaneously characterizes a protein's structure and its intrinsic dynamics⁠⁠. Ideally, such an approach could solely rely on RDC data-carrying both structural and dynamical information. The major bottleneck in the utilization of RDC data in recent years has been attributed to a lack of RDC analysis tools capable of extracting the pertinent information embedded within this complex source of data.  

Here we present a comprehensive strategy for structure calculation and reconstruction of discrete state dynamics from RDC data based on the SVD method of order tensor estimation. In addition to structure determination, we provide a mechanism of producing an ensemble of conformations for the dynamical regions of a protein from RDC data. The developed methodology has been tested on simulated RDC data with ±1Hz of error from an 83 residue α protein (PDB ID 1A1Z). In nearly all instances, our method reproduced the protein structure, including the conformational ensemble, to within less than 2Å. Based on our investigations, arc motions with more than 30° of rotation are recognized as internal dynamics and are reconstructed with sufficient accuracy.  Furthermore, states with relative occupancies above 20% are consistently recognized and reconstructed successfully. Arc motions with a magnitude of 15° or relative occupancy of less than 10% are consistently unrecognizable as dynamical regions within the context of ±1Hz of error.  

 We also introduce a computational approach named REDCRAFT that allows for uncompromised and concurrent characterization of protein structure and dynamics. We have subjected DHFR (PDB-ID 1RX2), a 159-residue protein, to a fictitious but plausible, mixed-mode internal dynamics model. In this simulation, DHFR was segmented into 7 regions. The two dynamical and rigid-body segments experienced an average orientational modification of 7˚ and 12˚, respectively. Observable RDC data for backbone C'-N, N-H, and C'-H were generated from 102 frames that described the molecular trajectory. The Dynamic Profile generated by REDCRAFT allowed for the recovery of individual fragments with bb-rmsd of less than 1Å and the identification of different dynamical regions of the protein. Following the recovery of fragments, structural assembly correctly assembled the four rigid fragments with respect to each other, categorized the two domains that underwent rigid-body dynamics, and identified one dynamical region for which no conserved structure can be defined. In conclusion, our approach successfully identified dynamical domains, recovery of structure where it is meaningful, and relative assembly of the domains when possible.