His super(73), Often Methylated, Is an Important Structural Determinant for Actin. A Mutagenic Analysis of His super(73) of Yeast Actin

• Published in: The Journal of biological chemistry Vol. 274; no. 52; pp. 37443 - 37449
• Main Authors: Yao, X, GraDe, S, Wriggers, W, Rubenstein, P A
• Format: Journal Article
• Language: English
• Published: 01.12.1999
• Subjects: Saccharomyces cerevisiae
• ISSN: 0021-9258
• DOI: 10.1074/jbc.274.52.37443

His super(73), has been proposed to regulate the release of P sub(i) from the interior of actin following polymerization-dependent hydrolysis of bound ATP. Although it is a 3-methylhistidine in the vast majority of actins, His super(73) is unmethylated in S. cerevisiae actin. We mutated His super(73) in yeast actin to Arg, Lys, Ala, Gln, and Glu and detected no altered phenotypes associated with the mutations in vivo. However, they significantly affect actin function in vitro. Substitution of the more basic residues resulted in enhanced thermal stability, decreased rate of nucleotide exchange, and decreased susceptibility to controlled proteolysis relative to wild-type actin. The opposite effects are observed with the neutral and anionic substitutions. All mutations reduced the rate of polymerization. Molecular dynamics simulations predict a new conformation for the His super(73) imidazole in the absence of a methyl group. It also predicts that Arg super(73) tightens and stabilizes the actin and that Glu super(73) causes a rearrangement of the bottom of actin's interdomain cleft leading possibly to our observed destabilization of actin. Considering the exterior location of His super(73), this work indicates a surprisingly important role for the residue as a major structural determinant of actin and provides a clue to the impact caused by methylation of His super(73).