title: Ca2+ regulation of gelsolin by its C-terminal tail.
abstract: Gelsolin is activated by Ca(2+) to sever actin filaments. Ca(2+) regulation is conferred on the N-terminal half by the C-terminal half. This paper seeks to understand how Ca(2+) regulates gelsolin by testing the "tail helix latch hypothesis," which is based on the structural data showing that gelsolin has a C-terminal tail helix that contacts the N-terminal half in the absence of Ca(2+). Ca(2+) activation of gelsolin at 37 degrees C occurs in three steps, with apparent K(d) for Ca(2+) of 0.1, 0.3, and 6.4 x 10(-6) m. Tail helix truncation decreases the apparent Ca(2+) requirement for severing to 10(-7) m and eliminates the conformational change observed at 10(-6) m Ca(2+). The large decrease in Ca(2+) requirement for severing is not due to a change in Ca(2+) binding nor to Ca(2+)-independent activation of the C-terminal half per se. Thus, the tail helix latch is primarily responsible for transmitting micromolar Ca(2+) information from the gelsolin C-terminal half to the N-terminal half. Occupation of submicromolar Ca(2+)-binding sites primes gelsolin for severing, but gelsolin cannot sever because the tail latch is still engaged. Unlatching the tail helix by 10(-6) m Ca(2+) releases the final constraint to initiate the severing cascade.
authors.affiliation: Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Lin
authors.forename: M
authors.initials: M
authors.lastname: Mejillano
authors.forename: H L
authors.initials: HL
authors.lastname: Yin
mesh_terms: D000199:Actins / Q000378:metabolism; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism*; D004533:Egtazic Acid / Q000494:pharmacology; D005341:Fibrinolysin; D018260:Gelsolin / Q000737:chemistry* / Q000378:metabolism*; D005978:Glutathione; D006801:Humans; D010084:Oxidation-Reduction; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017384:Sequence Deletion; D013816:Thermodynamics
chemical_list: D000199:Actins; D018260:Gelsolin; D010446:Peptide Fragments; D011994:Recombinant Proteins; D004533:Egtazic Acid; D005341:Fibrinolysin; D005978:Glutathione; D002118:Calcium