Abstract

The gene-3 protein (G3P) of filamentous phages is essential for the infection of Escherichia coli. The carboxy-terminal domain anchors this protein in the phage coat, whereas the two amino-terminal domains N1 and N2 protrude from the phage surface. We analyzed the folding mechanism of the two-domain fragment N1-N2 of G3P (G3P(*)) and the interplay between folding and domain assembly. For this analysis, a variant of G3P(*) was used that contained four stabilizing mutations (IIHY-G3P(*)). The observed refolding kinetics extend from 10 ms to several hours. Domain N1 refolds very rapidly (with a time constant of 9.4 ms at 0.5 M guanidinium chloride, 25 degrees C) both as a part of IIHY-G3P(*) and as an isolated protein fragment. The refolding of domain N2 is slower and involves two reactions with time constants of seven seconds and 42 seconds. These folding reactions of the individual domains are followed by a very slow, spectroscopically silent docking process, which shows a time constant of 6200 seconds. This reaction was detected by a kinetic unfolding assay for native molecules. Before docking, N1 and N2 unfold fast and independently, after docking they unfold slowly in a correlated fashion. A high energy barrier is thus created by domain docking, which protects G3P kinetically against unfolding. The slow domain docking is possibly important for the infection of E.coli by the phage. Upon binding to the F pilus, the N2 domain separates from N1 and the binding site for TolA on domain N1 is exposed. Since domain reassembly is so slow, this binding site remains accessible until pilus retraction has brought N1 close to TolA on the bacterial surface. Study holds ProTherm entries: 16098, 16099, 16100 Extra Details: N2 domain. IIHF-G3P* contains four Trp and 15 Tyr residues, and three Trp residues are in the N1 domain, and only one. W181, is in N2 at a solvent exposed position. Twelve Tyr residues are located within domain N2.,The denaturation process were observed by the fluorescence at 310 nm after excitation at 280 nm (to observe Tyr) to follow N2 domain. protein folding; folding kinetics; gene-3 protein; domain docking; pilus

Submission Details

ID: iAgjydeF

Submitter: Connie Wang

Submission Date: April 24, 2018, 8:47 p.m.

Version: 1

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