PEDS Advance Access originally published online on March 24, 2005
Protein Engineering Design and Selection 2005 18(2):103-110; doi:10.1093/protein/gzi004
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G protein-coupled receptors show unusual patterns of intrinsic unfolding
1Institute of Biotechnology (Biocenter 3), University of Helsinki, PO Box 65, Viikinkaari 1, FIN-00014 Helsinki, Finland, 2Viikki Graduate School in BioSciences, PO Box 56, Viikinkaari 9, FIN-00014 Helsinki, Finland, 3Department of Biological Services and 4Department of Structural Biology, Weizmann Institute of Science, 76100 Rehovot, Israel
5 To whom correspondence should be addressed. E-mail: adrian.goldman{at}helsinki.fi
Intrinsically unstructured proteins (IUPs) or IUP-like regions often play key roles in controlling processes ranging from transcription to the cell cycle. In silico such proteins can be identified by their sequence properties; they have low hydrophobicity and high net charge. In this study, we applied the FoldIndex (http://bioportal.weizmann.ac.il/fldbin/findex) program to analyze human G protein-coupled receptors and compared them with membrane proteins of known structure and with IUPs. We show that human G protein-coupled receptor (GPCR) extramembranous domains include long (>50 residues) disordered segments, unlike membrane proteins of known structure. The predicted disorder occurred primarily in the N-terminal, C-terminal and third intracellular domain regions: 55, 69 and 56% of the human GPCRs were disordered in these regions, respectively. This increased flexibility may therefore be critical for GPCR function. Surprisingly, however, the kinds of residues used in GPCR unstructured regions were different than in hitherto-identified IUPs. The GPCR third intracellular loop domains contain very high percentages of Arg, Lys and His residues, especially Arg, but the percentage of Glu, Asp and Pro is no higher than in folded proteins. We propose that this has structural and functional consequences.
Received January 18, 2005; accepted January 28, 2005.
Edited by Mirek Cygler
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