A ten-residue domain (Y11-A20) in the NH2-terminus modulates membrane association of annexin A7.
Annexin A7 (synexin, annexin VII) is postulated to promote membrane fusion during surfactant secretion in alveolar type II cells and catecholamine secretion in adrenal chromaffin cells. Recently, we demonstrated that the 1-29 residues in the NH(2)-terminus could, possibly by interaction with the COOH-terminus, influence the Ca(2+)-dependent membrane binding, aggregation, and fusion properties of annexin A7 (A7). In this study, we further investigated this 29-residue domain by evaluating several deletion and point mutations for membrane-associated functions of A7. In comparison to A7, the mutants lacking 1-29 residues (A7Delta(1-29)) or 1-21 residues (A7Delta(1-21)), but not those lacking 1-10 residues (A7Delta(1-10)) or 21-29 residues (A7Delta(21-29)), showed diminished membrane binding. Segmental deletion of 10-20 residues (A7Delta(10-20)) also decreased the protein binding to membranes. The Ca(2+)-dependent membrane aggregation of PLV with A7Delta(1-29) was maximally diminished but less so with A7Delta(10-20) or A7Delta(1-21) in comparison to that with A7. However, phospholipid vesicle (PVL) aggregation was unaffected with A7Delta(1-10) or A7Delta(21-29). The Ca(2+)-dependent membrane fusion of PLV was also diminished with A7Delta(10-20) and A7Delta(1-29), but not with A7Delta(1-10). Since the mode of annexin A7 association and function with biological membranes could be different, we also evaluated these proteins for functional changes with isolated lung lamellar bodies. In comparison to A7, the binding to lamellar bodies was diminished for A7Delta(1-29) and A7Delta(1-21) but not for A7Delta(1-10). The Ca(2+)-dependent fusion of isolated lamellar bodies with PLV was also diminished with A7Delta(1-29), but not with A7Delta(10-20) or A7Delta(1-21). Taken together, our studies suggest that the 10-residue domain (Y(11)-A(20)) in the NH(2)-terminus modifies the phospholipid binding and aggregation properties of annexin A7. For binding and fusion of biological membranes, the 10-29-residue domain may be required although the annexin A7 properties are primarily modulated through the Y(11)-A(20) domain.
Chander
Avinash
A
Department of Pediatrics, Stony Brook University School of Medicine, Stony Brook, NY 11794-8111, USA. ajerath@notes.cc.sunysb.edu
Naidu
Devendra G
DG
Chen
Xiao-Liang
XL
D000818:Animals; D017310:Annexin A7 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D008561:Membrane Fusion; D009154:Mutation; D011485:Protein Binding; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013329:Structure-Activity Relationship
D017310:Annexin A7; D011994:Recombinant Proteins