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Determinants of the broad recognition of exocytic Rab GTPases by Mss4

UMMS Affiliation

Graduate School of Biomedical Sciences; Program in Molecular Medicine



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Medical Subject Headings

Amino Acid Sequence; Animals; Anthranilic Acids; Crystallography, X-Ray; DNA Mutational Analysis; Electrostatics; Exocytosis; GTP Phosphohydrolase-Linked Elongation Factors; *Guanine Nucleotide Exchange Factors; Guanosine Diphosphate; Kinetics; Molecular Sequence Data; Mutagenesis, Site-Directed; Proteins; Rats; *Saccharomyces cerevisiae Proteins; Sequence Alignment; rab GTP-Binding Proteins; rab3A GTP-Binding Protein


Life Sciences | Medicine and Health Sciences


Rab GTPases function as essential regulators of vesicle transport between subcellular compartments of eukaryotic cells. Mss4, an evolutionarily conserved Rab accessory factor, facilitates nucleotide release and binds tightly to the nucleotide-free form of exocytic but not endocytic Rab GTPases. A structure-based mutational analysis of residues that are conserved only in exocytic Rab GTPases reveals three residues that are critical determinants of the broad specificity recognition of exocytic Rab GTPases by Mss4. One of these residues is located at the N-terminus of the switch I region near the nucleotide binding site whereas the other two flank an exposed hydrophobic triad previously implicated in effector recognition. The spatial disposition of these residues with respect to the structure of Rab3A correlates with the dimensions of the elongated Rab interaction epitope in Mss4 and supports a mode of interaction similar to that of other exchange factor-GTPase complexes. The complementarity of the corresponding interaction surfaces suggests a hypothetical structural model for the complex between Mss4 and Rab GTPases.

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Citation: Biochemistry. 2001 Dec 25;40(51):15699-706.

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