Analysis of tryptic digests indicates regions of GvpC that bind to gas vesicles of Anabaena flos-aquae

1 School of Biological Sciences, University of Bristol, Bristol BS8 1UG, UK 2 Department of Biochemistry, University of Bristol, Bristol BS8 1UG, UK Correspondence Anthony E. Walsby a.e.walsby{at}bristol.ac.uk The gas vesicles of the cyanobacterium Anabaena flos-aquae contain two main proteins: GvpA, which forms the ribs of the hollow cylindrical shell, and GvpC, which occurs on the outer surface. Analysis by MALDI-TOF MS shows that after incubating Anabaena gas vesicles in trypsin, GvpA was cleaved only at sites near the N-terminus, whereas GvpC was cleaved at most of its potential tryptic sites. Many of the resulting tryptic peptides from GvpC remained attached to the underlying GvpA shell: the pattern of attachment indicated that there are binding sites to GvpA at both ends of the 33-residue repeats (33 RR s) in GvpC, although one of the tryptic peptides within the 33 RR did not remain attached. Tryptic peptides near the two ends of the GvpC molecule were also lost. The mean critical collapse pressure of Anabaena gas vesicles decreased from 0.63 MPa to 0.20 MPa when GvpC was removed with urea or fully digested with trypsin; partial digestion resulted in partial decrease in critical pressure. Abbreviations: 33 RR , 33-residue repeat; M i , monoisotopic mass; MALDI-TOF, matrix assisted laser desorption ionization-time of flight