Structure of human annexin a6 at the air-water interface and in a membrane-bound state.
We postulate the existence of a pH-sensitive domain in annexin A6 (AnxA6), on the basis of our observation of pH-dependent conformational and orientation changes of this protein and its N- (AnxA6a) and C-terminal (AnxA6b) halves in the presence of lipids. Brewster angle microscopy shows that AnxA6, AnxA6a, and AnxA6b in the absence of lipids accumulate at the air-water interface and form a stable, homogeneous layer at pH below 6.0. Under these conditions polarization modulation IR absorption spectroscopy reveals significant conformational changes of AnxA6a whereas AnxA6b preserves its alpha-helical structure. The orientation of protein alpha-helices is parallel with respect to the interface. In the presence of lipids, polarization modulation IR reflection absorption spectroscopy experiments suggest that AnxA6a incorporates into the lipid/air interface, whereas AnxA6b is adsorbed under the lipid monolayer. In this case AnxA6a regains its alpha-helical structures. At a higher pressure of the lipid monolayer the average orientation of the alpha-helices of AnxA6a changes from flat to tilted by 45 degrees with respect to normal to the membrane interface. For AnxA6b no such changes are detected, even at a high pressure of the lipid monolayer-suggesting that the putative pH-sensitive domain of AnxA6 is localized in the N-terminal half of the protein.
Department of Cellular Biochemistry, Nencki Institute of Experimental Biology, Warsaw, Poland.
Marcin
M
Golczak
Aneta
A
Kirilenko
Joanna
J
Bandorowicz-Pikula
Bernard
B
Desbat
Slawomir
S
Pikula
D000327:Adsorption; D000388:Air; D017317:Annexin A6 / Q000737:chemistry*; D006801:Humans; D046911:Macromolecular Substances / Q000737:chemistry; D008560:Membrane Fluidity; D008563:Membrane Lipids / Q000737:chemistry*; D008565:Membrane Proteins / Q000737:chemistry*; D008567:Membranes, Artificial; D011485:Protein Binding; D011487:Protein Conformation; D013500:Surface Tension; D014867:Water / Q000737:chemistry*
D017317:Annexin A6; D046911:Macromolecular Substances; D008563:Membrane Lipids; D008565:Membrane Proteins; D008567:Membranes, Artificial; D014867:Water