β1 Integrin NPXY Motifs Regulate Kidney Collecting-Duct Development and Maintenance by Induced-Fit Interactions with Cytosolic Proteins

Loss of beta 1 integrin expression inhibits renal collecting-system development. Two highly conserved NPXY motifs in the distal beta 1 tail regulate integrin function by associating with phosphtyrosine binding (PTB) proteins, such as talin and kindlin. Here, we define the roles of these two tyrosines in collecting-system development and delineate the structural determinants of the distal beta 1 tail using nuclear magnetic resonance (NMR). Mice carrying alanine mutations have moderate renal collecting-system developmental abnormalities relative to beta 1-null mice. Phenylalanine mutations did not affect renal collecting-system development but increased susceptibility to renal injury. NMR spectra in bicelles showed the distal beta 1 tail is disordered and does not interact with the model membrane surface. Alanine or phenylalanine mutations did not alter beta 1 structure or interactions between alpha and beta 1 subunit transmembrane/cytoplasmic domains; however, they did decrease talin and kindlin binding. Thus, these studies highlight the fact that the functional roles of the NPXY motifs are organ dependent. Moreover, the beta 1 cytoplasmic tail, in the context of the adjacent transmembrane domain in bicelles, is significantly different from the more ordered, membrane-associated beta 1 integrin tail. Finally, tyrosine mutations of beta 1 NPXY motifs induce phenotypes by disrupting their interactions with critical integrin binding proteins like talins and kindlins.