Homology with vesicle fusion mediator syntaxin-1a predicts determinants of epimorphin/syntaxin-2 function in mammary epithelial morphogenesis.
We have shown that branching morphogenesis of mammary ductal structures requires the action of the morphogen epimorphin/syntaxin-2. Epimorphin, originally identified as an extracellular molecule, is identical to syntaxin-2, an intracellular molecule that is a member of the extensively investigated syntaxin family of proteins that mediate vesicle trafficking. We show here that, although epimorphin/syntaxin-2 is highly homologous to syntaxin-1a, only epimorphin/syntaxin-2 can stimulate mammary branching morphogenesis. We construct a homology model of epimorphin/syntaxin-2 based on the published structure of syntaxin-1a, and we use this model to identify the structural motif responsible for the morphogenic activity. We identify four residues located within the cleft between helices B and C that differ between syntaxin-1a and epimorphin/syntaxin-2; through site-directed mutagenesis of these four amino acids, we confer the properties of epimorphin for cell adhesion, gene activation, and branching morphogenesis onto the inactive syntaxin-1a template. These results provide a dramatic demonstration of the use of structural information about one molecule to define a functional motif of a second molecule that is related at the sequence level but highly divergent functionally.
Chen
Connie S
CS
Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
Nelson
Celeste M
CM
Khauv
Davitte
D
Bennett
Simone
S
Radisky
Evette S
ES
Hirai
Yohei
Y
Bissell
Mina J
MJ
Radisky
Derek C
DC
D020816:Amino Acid Motifs / Q000502:physiology; D019943:Amino Acid Substitution; D000818:Animals; D002448:Cell Adhesion / Q000502:physiology; D002460:Cell Line; D005260:Female; D006801:Humans; D008321:Mammary Glands, Animal / Q000196:embryology*; D042361:Mammary Glands, Human / Q000196:embryology*; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008958:Models, Molecular; D009024:Morphogenesis / Q000502:physiology*; D016297:Mutagenesis, Site-Directed; D040681:Structural Homology, Protein; D050827:Syntaxin 1 / Q000235:genetics / Q000378:metabolism*
C504582:Epim protein, mouse; D008562:Membrane Glycoproteins; C074558:STX2 protein, human; D050827:Syntaxin 1