Intermolecular interactions between cysteine and aromatic amino acids with phenyl moiety in the DNA-binding domain of heat shock factor 1 regulate thermal stress-induced trimerization.

In this study, we investigated the trimerization mechanism and structure of heat shock factor 1 (HSF1) in humans, goldfish, and walleye pollock at various temperatures. The trimerization of HSF1s were confirmed using western blotting using their respective antibodies. First, we examined the HSF1 DNA-binding domains of human (Homo sapiens), goldfish (Carassius auratus), and walleye pollock (Gadus chalcogrammus) by mutating key residues (36 and 103) that are thought to directly affect trimer generation. Humans, goldfish, and walleye pollock contain cysteine at residue 36, but cysteine (C), tyrosine (Y), and phenylalanine (F) at residue 103. Also, the trimer formation temperature of each species was found to be 42, 37, and 20 {degrees}C, respectively. In the mutation experiment, trimerization formed at 42 {degrees}C when residue 103 was C, at 37 {degrees}C it was Y, and at 20 {degrees}C it was F, regardless of the species. In addition, it was confirmed that when residue 103 of the three species was mutated to alanine (A), trimer was not formed. This suggest that, in addition to the previously identified C-C disulfide bonds in humans, C forms a trimer with a new type of bond with aromatic ring residues such as Y and F. Thus, HSF1 trimer formation temperature reveals the trimer creation mechanism through the fact that goldfish can have C-Y bonds at 37 {degrees}C, and walleye pollock can have C-F bonds at 20 {degrees}C. This study suggests that the trimer formation temperature and mechanism of HSF1 are regulated by the amino acid at residue 103.