Hayes C S, Illades-Aguiar B, Casillas-Martinez L, Setlow P
Department of Biochemistry, University of Connecticut Health Center, Farmington, Connecticut 06030, USA.
J Bacteriol. 1998 May;180(10):2694-700. doi: 10.1128/JB.180.10.2694-2700.1998.
Methionine residues in alpha/beta-type small, acid-soluble spore proteins (SASP) of Bacillus species were readily oxidized to methionine sulfoxide in vitro by t-butyl hydroperoxide (tBHP) or hydrogen peroxide (H2O2). These oxidized alpha/beta-type SASP no longer bound to DNA effectively, but DNA binding protected alpha/beta-type SASP against methionine oxidation by peroxides in vitro. Incubation of an oxidized alpha/beta-type SASP with peptidyl methionine sulfoxide reductase (MsrA), which can reduce methionine sulfoxide residues back to methionine, restored the alpha/beta-type SASP's ability to bind to DNA. Both tBHP and H2O2 caused some oxidation of the two methionine residues of an alpha/beta-type SASP (SspC) in spores of Bacillus subtilis, although one methionine which is highly conserved in alpha/beta-type SASP was only oxidized to a small degree. However, much more methionine sulfoxide was generated by peroxide treatment of spores carrying a mutant form of SspC which has a lower affinity for DNA. MsrA activity was present in wild-type B. subtilis spores. However, msrA mutant spores were no more sensitive to H2O2 than were wild-type spores. The major mechanism operating for dealing with oxidative damage to alpha/beta-type SASP in spores is DNA binding, which protects the protein's methionine residues from oxidation both in vitro and in vivo. This may be important in vivo since alpha/beta-type SASP containing oxidized methionine residues no longer bind DNA well and alpha/beta-type SASP-DNA binding is essential for long-term spore survival.
芽孢杆菌属α/β型小酸溶性芽孢蛋白（SASP）中的甲硫氨酸残基在体外易被叔丁基过氧化氢（tBHP）或过氧化氢（H₂O₂）氧化为甲硫氨酸亚砜。这些氧化的α/β型SASP不再能有效地与DNA结合，但DNA结合可在体外保护α/β型SASP免受过氧化物介导的甲硫氨酸氧化。将氧化的α/β型SASP与肽基甲硫氨酸亚砜还原酶（MsrA，可将甲硫氨酸亚砜残基还原回甲硫氨酸）一起孵育，可恢复α/β型SASP与DNA结合的能力。tBHP和H₂O₂均导致枯草芽孢杆菌芽孢中一种α/β型SASP（SspC）的两个甲硫氨酸残基发生一定程度的氧化，尽管在α/β型SASP中高度保守的一个甲硫氨酸仅被轻度氧化。然而，对携带对DNA亲和力较低的SspC突变形式的芽孢进行过氧化物处理会产生更多的甲硫氨酸亚砜。野生型枯草芽孢杆菌芽孢中存在MsrA活性。然而，msrA突变型芽孢对H₂O₂的敏感性并不比野生型芽孢更高。处理芽孢中α/β型SASP氧化损伤的主要机制是DNA结合，这在体外和体内均可保护蛋白质的甲硫氨酸残基不被氧化。这在体内可能很重要，因为含有氧化甲硫氨酸残基的α/β型SASP不再能很好地结合DNA，而α/β型SASP与DNA的结合对于芽孢的长期存活至关重要。
