Membrane-bound annexin V isoforms (CaBP33 and CaBP37) and annexin VI in bovine tissues behave like integral membrane proteins.
The distribution of annexin V isoforms (CaBP33 and CaBP37) and of annexin VI in bovine lung, heart, and brain subfractions was investigated with special reference to the fractions of these proteins which are membrane-bound. In addition to EGTA-extractable pools of the above proteins, membranes from lung, heart, and brain contain EGTA-resistant annexins V and VI which can be solubilized with detergents (Triton X-100 or Triton X-114). A strong base like Na2CO3, which is usually effective in extracting membrane proteins, only partially solubilizes the membrane-bound, EGTA-resistant annexins analyzed here. Also, only 50-60% of the Triton X-114-soluble annexins partition in the aqueous phase, the remaining fractions being recovered in the detergent-rich phase. Altogether, these findings suggest that, by an as yet unknown mechanism, following Ca(2+)-dependent association of annexin V isoforms and annexin VI with membranes, substantial fractions of these proteins remain bound to membranes in a Ca(2+)-independent way and behave like integral membrane proteins. These results further support the possibility that the above annexins might play a role in membrane trafficking and/or in the regulation of the structural organization of membranes.
Bianchi
R
R
Department of Experimental Medicine and Biochemical Sciences, University of Perugia, Italy.
Giambanco
I
I
Ceccarelli
P
P
Pula
G
G
Donato
R
R
D000818:Animals; D017304:Annexin A5; D017317:Annexin A6; D015153:Blotting, Western; D002135:Calcium-Binding Proteins / Q000737:chemistry*; D002417:Cattle; D014644:Genetic Variation; D008565:Membrane Proteins / Q000737:chemistry*; D011092:Polyethylene Glycols; D011257:Pregnancy Proteins / Q000737:chemistry*; D012995:Solubility; D013347:Subcellular Fractions / Q000737:chemistry; D014018:Tissue Distribution
D017304:Annexin A5; D017317:Annexin A6; D002135:Calcium-Binding Proteins; D008565:Membrane Proteins; D011257:Pregnancy Proteins; D011092:Polyethylene Glycols