Intra-helical salt-bridge and helix destabilizing residues within the same helical turn: Role of functionally important loop E half-helix in channel regulation of major intrinsic proteins

Biochimica Et Biophysica Acta
Ravi Kumar VermaRamasubbu Sankararamakrishnan

Abstract

The superfamily of major intrinsic proteins (MIPs) includes aquaporin (AQP) and aquaglyceroporin (AQGP) and it is involved in the transport of water and neutral solutes across the membrane. Diverse MIP sequences adopt a unique hour-glass fold with six transmembrane helices (TM1 to TM6) and two half-helices (LB and LE). Loop E contains one of the two conserved NPA motifs and contributes two residues to the aromatic/arginine selectivity filter. Function and regulation of majority of MIP channels are not yet characterized. We have analyzed the loop E region of 1468 MIP sequences and their structural models from six different organism groups. They can be phylogenetically clustered into AQGPs, AQPs, plant MIPs and other MIPs. The LE half-helix in all AQGPs contains an intra-helical salt-bridge and helix-breaking residues Gly/Pro within the same helical turn. All non-AQGPs lack this salt-bridge but have the helix destabilizing Gly and/or Pro in the same positions. However, the segment connecting LE half-helix and TM6 is longer by 10-15 residues in AQGPs compared to all non-AQGPs. We speculate that this longer loop in AQGPs and the LE half-helix of non-AQGPs will be relatively more flexible and this could be functionally important. Mo...Continue Reading

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Citations

Oct 19, 2005·Advances in Protein Chemistry·Jerry H Brown, Carolyn Cohen
Oct 16, 2016·Plant, Cell & Environment·Michael GroszmannJohn R Evans
Oct 27, 2017·Biochimica Et Biophysica Acta. Biomembranes·Margareta TrefzDirk Schneider

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