Comparative modeling of the N-terminal domain of the 67kDa laminin-binding protein: implications for putative ribosomal function.

Laminin-binding protein/p40 (LBP/p40) precursor appears to be involved in two seemingly unrelated activities-cell adhesion and ribosomal biogenesis. Analysis of primary structure revealed a two-domain organization of the LBP/p40. The N-terminal portion of LBP is similar to the S2 family of prokaryotic ribosomal proteins, while the C-terminus is unique for Metazoa and is involved in extraribosomal functions. To gain insight into putative ribosomal functions of LBP we performed comparative modeling of the N-terminal domain using crystal structures of S2p from Thermus thermophilus. The LBP model assumes an alpha-beta sandwich fold similar to that of S2. Modeling revealed the loss of a significant portion of ribosomal RNA (rRNA) interaction domain, lack of conservation of many residues involved in interactions with rRNA, and a major shift in surface charge distribution (compared to the S2 protein). The overall stability of the fold argues against a proposed transmembrane domain in the central part of the protein. Partial overlap in S2 and laminin-binding domains suggests that ribosomal and surface receptor functions would be mutually exclusive. The possible biological role of LBP/p40 bifunctionality is discussed.