The Role of Two SmXXXSm Motifs in the Dimerization of the FGFR3 Transmembrane Domain

Abstract

Fibroblast growth factor receptor 3 (FGFR3) is a single pass membrane protein and a member of the receptor tyrosine kinase (RTK) family of proteins. FGFR3 has three distinct domains: the ligand binding extracellular domain, the cytosolic kinase domain, and the transmembrane (TM) domain. Previous work with the isolated FGFR3 TM domains has shown that it has the ability to self-dimerize. The TM domain of FGFR3 has two adjacent SmXXXSm motifs in the sequence, where the Sm residues are Ala374, Ser378 and Gly382. The SmXXXSm motif has been shown to play an important role in helix- helix interaction in other transmembrane proteins such as GpA and BNIP3. Currently, we are using site directed mutagenesis and ToxR activity assays to analyze the importance of this sequence motif for the interaction between the helices. Single mutations were made at three specific points, changing the small amino acids (Ala374, Ser378, and Gly382) to five different amino acids (Ala, Cys, Gly, Ile, and Ser). Relative activity measurements were made comparing the activity of the mutant protein to that of the wild type protein. Through these comparative measurements we can assess their role in helix-helix interaction.