LIM DOMAINS OF CYSTEINE-RICH PROTEIN-1 (CRP1) ARE ESSENTIAL FOR ITS ZYXIN-BINDING FUNCTION

Previous studies have demonstrated that the adhesion-plaque protein, z yxin, interacts specifically with a 23 kDa protein, called the cystein e-rich protein 1 (CRP1), which has been implicated in myogenesis. Prim ary sequence analyses have revealed that both zyxin and CRP1 exhibit m ultiple copies of a structural motif called the LIM domain. LIM domain s, which are defined by the consensus CX2CX16-23HX2CX2CX2CX16-23CX2-3( C,H,D), are found in a variety of proteins that are involved in cell g rowth and differentiation. Recent studies have established that LIM do mains are zinc-binding structures that mediate specific protein-protei n interactions. For example, in the case of the zyxin-CRP1 interaction , one of zyxin's three LIM domains is necessary and sufficient for bin ding to CRP1. Because the CRP1 molecule is comprised primarily of two LIM domains, we were interested in the possibility that the binding si te for zyxin on CRP1 might also be contained within a single LIM domai n. Consistent with the hypothesis that the LIM domains of CRP1 are cri tical for the protein's zyxin-binding function, zinc-depleted CRP1 dis plays a reduced zyxin-binding activity. However, domain mapping analys es have revealed that neither of the two individual LIM domains of CRP 1 can support a wild-type interaction with zyxin. Collectively, our re sults suggest that the binding site for zyxin on CRP1 is not contained within a single contiguous sequence of amino acids, Instead, the inte raction appears to rely on the co-ordinate action of a number of resid ues that are displayed in both of CRP1's LIM domains.