Polyproline II conformation

Src tyrosine kinase contains both an SH2 and an SH3 domain linked to a tyrosine kinase unit with a structure similar to other protein kinases. The phosphorylated form of the kinase is inactivated by binding of a phosphoty-rosine in the C-terminal tail to its own SH2 domain. In addition the linker region between the SH2 domain and the kinase is bound in a polyproline II conformation to the SH3 domain. These interactions lock regions of the active site into a nonproductive conformation. Dephosphorylation or mutation of the C-terminal tyrosine abolishes this autoinactivation. 

Mykhailiuk PK, Afonin S, Palamarchuk GV, Shishkin OV, Ulrich AS, Komarov IV (2008) Synthesis of trifluoromethyl-substituted proline analogues as F-19 NMR labels for peptides in the polyproline II conformation. Angew Chem Int Edit 47 5765-5767... 

Bour and Keiderling (1993) report ah initio simulation of the vibrational circular dichroism of coupled peptides in the amide I and II region. Using the MFP model and the 4-3IG basis set they were able to reproduce the VCD sign pattern and the relative intensities of spectra of proteins in the a-helical, /)-sheet 3io-helical and polyproline II conformations. 

Asher, S.A., Mikhonin, A.V., and Bykov, S. UV Raman demonstrates that alpha-helical polyalanine peptides melt to polyproline II conformations, /. Am. Chem. Soc., 126, 8433, 2004. 

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