Fluorescence Correlation Spectroscopic Study of Serpin Depolymerization by Computationally Designed Peptides

Abstract

Members of the serine proteinase inhibitor (serpin) family play important roles in the inflammatory and coagulation cascades. Interaction of a serpin with its target proteinase induces a large conformational change, resulting in insertion of its reactive center loop (RCL) into the main body of the protein as a new strand within β-sheet A. Intermolecular insertion of the RCL of one serpin molecule into the β-sheet A of another leads to polymerization, a widespread phenomenon associated with a general class of diseases known as serpinopathies. Small peptides are known to modulate the polymerization process by binding within β-sheet A. Here, we use fluorescence correlation spectroscopy (FCS) to probe the mechanism of peptide modulation of α1-antitrypsin (α1-AT) polymerization and depolymerization, and employ a statistical computationally-assisted design strategy (SCADS) to identify new tetrapeptides that modulate polymerization. Our results demonstrate that peptide-induced depolymerization takes place via a heterogeneous, multi-step process that begins with internal fragmentation of the polymer chain. One of the designed tetrapeptides is the most potent antitrypsin depolymerizer yet found.