Eb. Babiychuk et A. Draeger, Annexins in cell membrane dynamics: Ca2+-regulated association of lipid microdomains, J CELL BIOL, 150(5), 2000, pp. 1113-1123
The sarcolemma of smooth muscle cells is composed of alternating stiff acti
n-binding, and flexible caveolar domains. In addition to these stable macro
-domains, the plasma membrane contains dynamic glycosphingolipid- and chole
sterol-enriched microdomains, which act as sorting posts for specific prote
ins and art: involved in membrane trafficking and signal transduction. We d
emonstrate that these lipid rafts are neither periodically organized nor ex
clusively confined to the actin attachment sites or caveolar regions. Chang
es in the Ca2+ concentration that are affected during smooth muscle contrac
tion lead to important structural rearrangements within the sarcolemma, whi
ch can be attributed to members of the annexin protein family. We show that
the associations of annexins II,V, and VI with smooth muscle microsomal me
mbranes exhibit a high degree of Ca2+ sensitivity, and that the extraction
of annexins II and VI by detergent is prevented by elevated Ca2+ concentrat
ions. Annexin VI participates in the formation of a reversible, membrane-cy
toskeleton complex (Babiychuk, E.B., R.J. Palstra, J. Schaller, U. Kampfer,
and A. Draeger. 1999. J. Biol. Chem. 274:35191-35195). Annexin II promotes
the Ca2+-dependent association of lipid raft microdomains, whereas annexin
V interacts with glycerophospholipid microcompartments. These interactions
bring about a new configuration of membrane-bound constituents, with poten
tially important consequences for signaling events and Ca2+ flux.