Heterogeneity in the Folding of Villin Headpiece Subdomain HP36

• DOI: 10.1021/acs.jpcb.8b07683
• Publication Date: 2018-08-17T19:24:15Z
• Authors: Sureshbabu Nagarajan; Shifeng Xiao; Daniel P. Raleigh; R. Brian Dyer
• Keywords: Villin; Folding (DSP implementation)

Small single domain proteins that fold on the microsecond time scale have been subject of intense interest as models for probing complexity folding energy landscapes. The villin headpiece subdomain (HP36) has extensively studied because its simple three helix structure, ultrafast lifetime a few microseconds, and stable native fold. We previously shown measured by 13C═18O isotopic label residue A57 in 2 occurs at different rate than global probes folding, indicating noncooperative HP36. In order to determine whether this reflects intermediates or parallel pathways over small activation barrier, labels were individually incorporated six positions HP36, including into all 3 helices. equilibrium thermal unfolding transitions folding/unfolding dynamics monitored using unique IR signature temperature dependent FTIR jump spectroscopy, respectively. Equilibrium experiments reveal HP36 show drastic differences midpoint their (Tm), ranging from 45 67 °C. Heterogeneity is also observed relaxation kinetics; there are phase when labeled probed. At final °C, 2.4e + 05 s–1 whereas L69 5.1e s–1, two times faster. observation site-dependent midpoints rates enables us probe progressive accumulation folded providing insight microscopic details mechanism.