title: Visual insight into how low pH alone can induce actin-severing ability in gelsolin under calcium-free conditions.
abstract: Gelsolin is a key actin cytoskeleton-modulating protein primarily regulated by calcium and phosphoinositides. In addition, low pH has also been suggested to activate gelsolin in the absence of Ca(2+) ions, although no structural insight on this pathway is available except for a reported decrement in its diffusion coefficient at low pH. We also observed ~1.6-fold decrease in the molecular mobility of recombinant gelsolin when buffer pH was lowered from 9 to 5. Analysis of the small angle x-ray scattering data collected over the same pH range indicated that the radius of gyration and maximum linear dimension of gelsolin molecules increased from 30.3 to 34.1 Å and from 100 to 125 Å, respectively. Models generated for each dataset indicated that similar to the Ca(2+)-induced process, low pH also promotes unwinding of this six-domain protein but only partially. It appeared that pH is able to induce extension of the G1 domain from the rest of the five domains, whereas the Ca(2+)-sensitive latch between G2 and G6 domains remains closed. Interestingly, increasing the free Ca(2+) level to merely ~40 nM, the partially open pH 5 shape "sprung open" to a shape seen earlier for this protein at pH 8 and 1 mm free Ca(2+). Also, pH alone could induce a shape where the g3-g4 linker of gelsolin was open when we truncated the C-tail latch from this protein. Our results provide insight into how under physiological conditions, a drop in pH can fully activate the F-actin-severing shape of gelsolin with micromolar levels of Ca(2+) available.
authors.affiliation: Renal, Electrolyte and Hypertension Division, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA. rgarg@imtech.res.in
authors.forename: Renu
authors.initials: R
authors.lastname: Garg
authors.forename: Nagesh
authors.initials: N
authors.lastname: Peddada
authors.forename: Amin
authors.initials: A
authors.lastname: Sagar
authors.forename: Deepak
authors.initials: D
authors.lastname: Nihalani
authors.lastname: Ashish
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D002118:Calcium; D018360:Crystallography, X-Ray; D018260:Gelsolin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D006863:Hydrogen-Ion Concentration; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship
chemical_list: D000199:Actins; D018260:Gelsolin; D002118:Calcium