S100A1 and S100B interactions with annexins

Members of the annexin protein family interact with members of the S100 pro tein family thereby forming heterotetramers in which an S100 homodimer cros sbridges two copies of the pertinent annexin. Previous work has shown that S100A1 and S100B bind annexin VI in a Ca2+-dependent manner and that annexi n VI, but not annexin V, blocks the inhibitory effect of S100A1 and S100B o n intermediate filament assembly. We show here that both halves of annexin VI (i.e., the N-terminal half or annexin VI-a and the C-terminal half or an nexin VI-b) bind individual S100s on unique sites and that annexin VI-b, bu t not annexin VI-a, blocks the ability of S100A1 and S100B to inhibit inter mediate filament assembly. We also show that the C-terminal extension of S1 00A1 (and, by analogy, S100B), that was previously demonstrated to be criti cal for S100A1 and S100B binding to several target proteins including inter mediate filament subunits, is not part of the S100 surface implicated in th e recognition of annexin VI, annexin VI-a, or annexin VI-b. Evaluation of f unctional properties with a liposome stability and a calcium influx assay r eveals the ability of both S100 proteins to permeabilize the membrane bilay er in a similar fashion like annexins. When tested in combinations with dif ferent annexin proteins both S100 proteins mostly lead to a decrease in the calcium influx activity although not all annexin/S100 combinations behave in the same manner. Latter observation supports the hypothesis that the S10 0-annexin interactions differ mechanistically depending on the particular p rotein partners. (C) 2000 Elsevier Science B.V. All rights reserved.