Cell Migration on Compliant Substrates Requires Actin Polymerization by the Arp2/3 Complex

Abstract

VCD thermal equilibrium spectroscopic studies are supported by NMR-based structures and DFT modeling. MD dynamics simulations are correlated with IR-detected temperature-jump kinetics. These all have b-sheet structures, but differ in stabilities for different turns and aromatic contacts. DFT computations for an Ala-based structure with NMR constrained f,c angles yield IR and VCD simulations consistent with experimental data. The structures are sharply twisted with the first hairpin being better formed. Aromatic stabilization was energetically effective for Trp-Tyr on strands 1-2, less on strands 2-3, but a similar sequence with no aromatic interactions formed better sheets. MD studies show bistable fluctuation in the D Pro-Gly turns from Type 1' to 2', but Aib-Gly turns, with less torsional barrier, sampled more forms. These behaviors were evident in site-selected IR-detected T-jump relaxation kinetics. Isotopic labeling allows selected monitoring of turns and strands, and Aib-Gly have less spectral interference than D Pro-Gly turns. Equilibrium IR as well as T-jump dynamics reflect higher stabilities for strand 1-2 interactions.