Profilin-actin complexes directly elongate actin filaments at the barbed end.
We demonstrate that the profilin-G-actin complex can elongate actin filaments directly at the barbed end but cannot bind to the pointed end. During elongation, the profilin-actin complex binds to the barbed filament end, whereupon profilin is released, leaving the actin molecule behind. This was first proposed by Tilney [Tilney, L. G., et al. (1983) J. Cell Biol. 97, 112-124] and demonstrated by Pollard and Cooper [(1984) Biochemistry 23, 6631-6641] by electron microscopy. We show that a model without any outside energy supply, in contrast to the mechanism proposed by Pollard and Cooper, can be fitted to our and their [Kaiser et al. (1986) J. Cell Biol. 102, 221-226] findings. Input of outside energy is necessary only if profilin-mediated elongation continues after free G-actin has been lowered to or below the critical concentration observed at the barbed end in the absence of profilin.
Pring
M
M
Department of Physiology, University of Pennsylvania, Philadelphia 19104.
Weber
A
A
Bubb
M R
MR
D000048:Acanthamoeba / Q000737:chemistry; D000177:Acrosome / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000818:Animals; D003285:Contractile Proteins; D006737:Horseshoe Crabs; D007700:Kinetics; D008297:Male; D008433:Mathematics; D008840:Microfilament Proteins / Q000378:metabolism*; D011108:Polymers; D051304:Profilins; D011721:Pyrenes / Q000378:metabolism; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
D000199:Actins; D003285:Contractile Proteins; D008840:Microfilament Proteins; D011108:Polymers; D051304:Profilins; D011721:Pyrenes