Role of the C-terminal SH3 domain and N-terminal tyrosine phosphorylation in regulation of Tim and related Dbl-family proteins.
Dbl-related oncoproteins are guanine nucleotide exchange factors (GEFs) specific for Rho-family GTPases and typically possess tandem Dbl (DH) and pleckstrin homology (PH) domains that act in concert to catalyze exchange. Although the exchange potential of many Dbl-family proteins is constitutively activated by truncation, the precise mechanisms of regulation for many Dbl-family proteins are unknown. Tim and Vav are distantly related Dbl-family proteins that are similarly regulated; their Dbl homology (DH) domains interact with N-terminal helices to exclude and prevent activation of Rho GTPases. Phosphorylation, substitution, or deletion of the blocking helices relieves this autoinhibition. Here we show that two other Dbl-family proteins, Ngef and Wgef, which like Tim contain a C-terminal SH3 domain, are also activated by tyrosine phosphorylation of a blocking helix. Consequently, basal autoinhibition of DH domains by direct steric exclusion using short N-terminal helices likely represents a conserved mechanism of regulation for the large family of Dbl-related proteins. N-Terminal truncation or phosphorylation of many other Dbl-family GEFs leads to their activation; similar autoinhibition mechanisms could explain some of these events. In addition, we show that the C-terminal SH3 domain binding to a polyproline region N-terminal to the DH domain of the Tim subgroup of Dbl-family proteins provides a unique mechanism of regulated autoinhibition of exchange activity that is functionally linked to the interactions between the autoinhibitory helix and the DH domain.
Yohe
Marielle E
ME
Department of Pharmacology, Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, North Carolina 27599-7295, USA.
Rossman
Kent
K
Sondek
John
J
D000595:Amino Acid Sequence; D000818:Animals; D019556:COS Cells; D018797:Cell Cycle Proteins / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D002522:Chlorocebus aethiops; D020558:GTP Phosphohydrolases / Q000737:chemistry / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry* / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D018909:src Homology Domains; D019061:src-Family Kinases / Q000378:metabolism
D018797:Cell Cycle Proteins; D020662:Guanine Nucleotide Exchange Factors; D047908:Intracellular Signaling Peptides and Proteins; C509769:TIMELESS protein, human; D019000:Phosphotyrosine; D019061:src-Family Kinases; D020558:GTP Phosphohydrolases