Characterization of a novel interaction between the calcium(2+)-binding protein S100A11 and the calcium(2+)- and phospholipid-binding protein annexin A6 of smooth muscle.

摘要

S100A11, an EF-hand-containing Ca2+-binding protein, undergoes a conformational change upon binding Ca2+, with exposure of a hydrophobic surface for interaction with a target protein(s). A novel Ca 2+-dependent interaction between S100A11 and the Ca2+- and phospholipid-binding protein annexin A6 of smooth muscle was identified by affinity chromatography, gel overlay, co-sedimentation with liposomes and chemical cross-linking. The expression of S100A11 and annexin A6 in smooth muscle was confirmed by RT-PCR and Western blotting. S100A11-binding sites were identified in both N- and C-terminal domains of annexin A6 by deletion mutagenesis and partial tryptic digestion. The unique N-terminal head region of annexin A6 was not required for Ca2+-dependent binding to S100A11. The S100A11-annexin A6 interaction, which was disrupted by phosphorylation of S100A11 at Thr9 by Ca2+-dependent protein kinase C, may play a role in control of membrane-cytoskeleton connections, which are necessary for force development, and/or control of formation of signaling complexes at the sarcolemma.