Molecular dissection of a LIM domain

LIM domains are novel sequence elements that are found in more than 60 gene products, many of which function as key regulators of developmental pathways. The LIM domain, characterized by the cysteine-rich consensus CX(2)CX(16-23)HX(2)CX(2)CX(2)CX(16-21)CX(2-3)(C/H/D), is a specific metal-binding structure that consists of two distinct zinc-binding subdomains. We and others have recently demonstrated that the LIM domain mediates protein-protein interactions. However, the sequences that define the protein-binding specificity of the LIM domain had not yet been identified. Because structural studies have revealed that the C-terminal zinc-binding module of a LIM domain displays a tertiary fold compatible with nucleic acid binding, it was of interest to determine whether the specific protein-binding activity of a LIM domain could be ascribed to one of its two zinc-binding subdomains. To address this question, we have analyzed the protein-binding capacity of a model LIM peptide, called zLIM1, that is derived from the cytoskeletal protein zyxin. These studies demonstrate that the protein-binding function of zLIM1 can be mapped to sequences contained within its N-terminal zinc-binding module. The C-terminal zinc-binding module of zLIM1 may thus remain accessible to additional interactive partners. Our results raise the possibility that the two structural subdomains of a LIM domain are capable of performing distinct biochemical functions.