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 developmen tal pathways. The LIM domain, characterized by the cysteine-rich conse nsus 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 sub domains. We and others have recently demonstrated that the LIM domain mediates protein-protein interactions. However, the sequences that def ine the protein-binding specificity of the LIM domain had not yet been identified. Because structural studies have revealed that the C-termi nal zinc-binding module of a LIM domain displays a tertiary fold compa tible with nucleic acid binding, it was of interest to determine wheth er the specific protein-binding activity of a LIM domain could be ascr ibed to one of its two zinc-binding subdomains. To address this questi on, we have analyzed the protein-binding capacity of a model LIM pepti de, 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-bindin g module. The C-terminal zinc-binding module of zLIM1 may thus remain accessible to additional interactive partners. Our results raise the p ossibility that the two structural subdomains of a LIM domain are capa ble of performing distinct biochemical functions.