Poster: Membrane transport

Abs # 177: Analysis of the putative pore-selectivity regions of Arabidopsis Major Intrinsic Proteins by Homology Modeling

Presenter:	Wallace, Ian S, iwallace@utk.edu
Authors	Wallace, Ian S (A)   Roberts, Daniel M (A)
Affiliations:	(A): University Of Tennessee

Major intrinsic proteins (MIPs) are a family of membrane channels that facilitate the bidirectional transport of water and small uncharged solutes such as glycerol. Using computational methods we have constructed homology models of the putative pore regions for the 35 full-length MIPs of Arabidopsis thaliana using the X-ray crystal structures of mammalian aquaporin1 and the bacterial glycerol permease, GlpF as templates. Based on comparisons of the narrow selectivity filter regions of the pores (the aromatic/arginine filter or ar/R region), the members of the four phylogenetic subfamilies of Arabidopsis MIPs can be classified into eight subgroups. PIP proteins possesss a uniform ar/R signature characteristic of high water transport aquaporins, whereas the TIP subfamily is highly diverse with three separate conserved ar/R regions. NIPs possess two separate conserved ar/R regions, one which is similar to the archetype, soybean (Glycine max) nodulin 26, and another which is characteristic of Arabidopsis NIP6;1. The SIP subfamily possesses two ar/R subgroups, characteristic of either SIP1 or SIP2. The residues of both SIP ar/R subgroups are divergent from MIPs in plants and other kingdoms. Overall, these findings suggest that higher plants MIPs have a common fold but show distinct differences in pore apertures, potential to form hydrogen bonds with transported molecules, and amphiphilicity that likely result in divergent transport selectivities. (Supported by an ASPB SURF award to ISW and by NSF grant MCB-0237219).