Long-range conformational effects of proteolytic removal of the last three residues of actin.
Truncated derivatives of actin devoid of either the last two (actin-2C) or three residues (actin-3C) were used to study the role of the C-terminal segment in the polymerization of actin. The monomer critical concentration and polymerization rate increased in the order: intact actin < actin-2C < actin-3C. Conversely, the rate of hydrolysis of actin-bound ATP during spontaneous polymerization of Mg-actin decreased in the same order, so that, for actin-3C, the ATP hydrolysis significantly lagged behind the polymer growth. Probing the conformation of the nucleotide site in the monomer form by measuring the rates of the bound nucleotide exchange revealed a similar change upon removal of either the two or three residues from the C-terminus. The C-terminal truncation also resulted in a slight decrease in the rate of subtilisin cleavage of monomeric actin within the DNAse-I binding loop, whereas in F-actin subunits the susceptibility of this and of another site within this loop, specifically cleaved by a proteinase from Escherichia coli A2 strain, gradually increased upon sequential removal of the two and of the third residue from the C-terminus. From these and other observations made in this work it has been concluded that perturbation of the C-terminal structure in monomeric actin is transmitted to the cleft, where nucleotide and bivalent cation are bound, and to the DNAse-I binding loop on the top of subdomain 2. Further changes at these sites, observed on the polymer level, seem to result from elimination of the intersubunit contact between the C-terminal residues and the DNAse-I binding loop. It is suggested that formation of this contact plays an essential role in regulating the hydrolysis of actin-bound ATP associated with the polymerization process.
Strzelecka-Gołaszewska
H
H
Department of Muscle Biochemistry, Nencki Institute of Experimental Biology, Warsaw, Poland.
Mossakowska
M
M
Woźniak
A
A
Moraczewska
J
J
Nakayama
H
H
D000199:Actins / Q000737:chemistry* / Q000378:metabolism; D000818:Animals; D001704:Biopolymers; D006868:Hydrolysis; D018482:Muscle, Skeletal / Q000737:chemistry; D009711:Nucleotides / Q000737:chemistry; D011487:Protein Conformation; D011817:Rabbits
D000199:Actins; D001704:Biopolymers; D009711:Nucleotides