Heintz D, Reichert A, Mihelic-Rapp M, Stoeva S, Voelter W, Faulstich H
Max-Planck-Institut für Medizinische Forschung, Heidelberg, Germany.
Eur J Biochem. 1994 Jul 15;223(2):345-50. doi: 10.1111/j.1432-1033.1994.tb19000.x.
Thymosin beta 4 (T beta 4), a peptide of 43 amino acids, binds to actin monomers and inhibits filament formation. In preparations of T beta 4 from bovine lung tissue, the peptide is accompanied by a derivative in which the methionine residue in position 6 is replaced by its sulfoxide. T beta 4 sulfoxide inhibits actin polymerization to an extent approximately 20-times less than T beta 4. While an equimolar amount of T beta 4 prevented actin polymerization almost completely, polymerization with the corresponding amount of the sulfoxide proceeded in a manner similar to that of pure actin, except for a slight retardation. We showed that the decrease in the inhibitory activity is reflected by a 20-times lower affinity to actin. Interestingly, under non-polymerizing conditions, the affinity of T beta 4 sulfoxide for actin is as high as that of T beta 4 (approximately 1 microM). In accordance with this, no differences were found between T beta 4 and the sulfoxide in cross-linking experiments with the monomer, where both forms of the peptide yielded similar amounts of a 47-kDa band representing conjugates of actin and beta-thymosin, as proved by Western-blotting analysis. Likewise, both, T beta 4 and the sulfoxide retarded the exchange of G-actin-bound nucleotide to similar extents. Although the sulfoxide is presumably a product of autoxidation, it is attractive to speculate that oxidation of the methionine residue in T beta 4 may represent a regulatory switch for starting filament formation in non-muscle cells.
胸腺素β4（Tβ4）是一种由43个氨基酸组成的肽，它与肌动蛋白单体结合并抑制细丝形成。在从牛肺组织制备Tβ4的过程中，该肽伴随着一种衍生物，其中第6位的甲硫氨酸残基被其亚砜取代。Tβ4亚砜抑制肌动蛋白聚合的程度比Tβ4小约20倍。当等摩尔量的Tβ4几乎完全阻止肌动蛋白聚合时，与相应量的亚砜聚合的方式与纯肌动蛋白相似，只是略有延迟。我们发现抑制活性的降低反映在对肌动蛋白的亲和力降低了20倍。有趣的是，在非聚合条件下，Tβ4亚砜对肌动蛋白的亲和力与Tβ4一样高（约1 microM）。据此，在与单体的交联实验中，Tβ4和亚砜之间未发现差异，通过蛋白质印迹分析证明，两种形式的肽产生的代表肌动蛋白和β-胸腺素缀合物的47-kDa条带的量相似。同样，Tβ4和亚砜都在相似程度上延迟了G-肌动蛋白结合核苷酸的交换。尽管亚砜可能是自氧化的产物，但推测Tβ4中甲硫氨酸残基的氧化可能代表非肌肉细胞中启动细丝形成的调节开关，这很有吸引力。
