The sulfoxide of thymosin beta 4 almost lacks the polymerization-inhibiting capacity for actin.
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.
Heintz
D
D
Max-Planck-Institut für Medizinische Forschung, Heidelberg, Germany.
Reichert
A
A
Mihelic-Rapp
M
M
Stoeva
S
S
Voelter
W
W
Faulstich
H
H
D000199:Actins / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002417:Cattle; D002851:Chromatography, High Pressure Liquid; D003432:Cross-Linking Reagents; D004591:Electrophoresis, Polyacrylamide Gel; D007700:Kinetics; D008168:Lung / Q000378:metabolism; D008715:Methionine / Q000737:chemistry; D008840:Microfilament Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010084:Oxidation-Reduction; D011108:Polymers; D013454:Sulfoxides / Q000737:chemistry / Q000378:metabolism*; D013947:Thymosin / Q000737:chemistry / Q000378:metabolism*; D000099201:Thymosin beta(4)
D000199:Actins; D000255:Adenosine Triphosphate; D003432:Cross-Linking Reagents; D008715:Methionine; D008840:Microfilament Proteins; D011108:Polymers; D013454:Sulfoxides; D013947:Thymosin; D000099201:Thymosin beta(4)