The ternary complex of DNase I, actin and thymosin beta4.
We have recently described a method for identifying contact sites between actin and thymosin beta4 (Tbeta4) by following spectrophotometrically the extent and kinetics of distinct, thiol-specific crosslinking reactions between appropriate derivatives of the two proteins [Reichert et a]. (1996) J. Biol. Chem. 271, 1301-1308]. In the present study this method was used to show that such crosslinking, which is indicative of complex formation, occurs to the same extent with the actin-DNase I complex as with pure actin, although at a somewhat lower rate. Further evidence for the formation of the ternary complex was given by gel electrophoresis. From fluorescence spectroscopy the KD value of Tbeta4 from the actin-DNase I complex was found to be identical to that from pure actin. In line with these data, the capacity of actin for inhibiting DNase I was not affected by the addition of Tbeta4. In conclusion, DNase I and Tbeta4 are independent of each other in their interaction with actin, suggesting that the binding sites of thymosin beta4 and DNase I on actin do not overlap. A ternary complex of DNase I, actin and Tbeta4, if obtained in crystalline form, could thus provide an approach for studying the interface of Tbeta4 and actin by X-ray analysis.
Reichert
A
A
Max-Planck-Institut für medizinische Forschung, Heidelberg, Germany.
Heintz
D
D
Echner
H
H
Voelter
W
W
Faulstich
H
H
D000199:Actins / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D003432:Cross-Linking Reagents; D003850:Deoxyribonuclease I / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015394:Molecular Structure; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D013947:Thymosin / Q000378:metabolism*; D000099201:Thymosin beta(4)
D000199:Actins; D003432:Cross-Linking Reagents; D003850:Deoxyribonuclease I; D013947:Thymosin; D000099201:Thymosin beta(4)