Modulation of Human Small Heat Shock Proteins via Changes in Quasi-ordered Networks of Interactions

Abstract

Small heat shock proteins (sHSPs) are molecular chaperones found in all domains of life that directly interact with client proteins to maintain them in a soluble and functional state. sHSPs are among the earliest responders to cellular stress events associated with client destabilization, and failure to fully or properly respond leads to client protein aggregation. Protein aggregation is a hallmark of several known disease states, including fibrillar aggregation associated with neurodegenerative diseases and amorphous aggregation in the eye lens that causes cataract. sHSPs are finely tuned to the cellular environment and are modulated by conditions that are associated with stress, such as pH acidosis or change in redox state. While we understand that modulation of sHSPs’ chaperone activity and expression level occurs, the molecular details that underlie mechanisms of chaperone activity remain enigmatic, largely because sHSPs’ properties defy conventional structural analysis. Recent development of new methods and experimental approaches are beginning to shed light on this crucially important, yet poorly understood family of chaperones. This dissertation reveals how primary sequence changes in the two most highly-related human sHSPs, HSPB4 and HSPB5, affect their structure and dynamics, interactions, and ability to delay aggregation of lens client γD-crystallin. Chapter 2 reveals the molecular changes caused by two single-site mutations in HSPB5 that are associated with autosomal dominant inheritance of cataract and myopathy in human patients. Chapter 3 describes how sequence differences in the N-terminal region of human HSPB4 and HSPB5 affects their structure, dynamics, interactions, and ability to productively interact with γD-crystallin.