Oligomerization of water and solute channels of the major intrinsic protein (MIP) family (original) (raw)

2001, Kidney International

(250 to 290 amino acids), and the high conservation intrinsic protein (MIP) family. Water and small solute fluxes throughout the MIP family may indicate a common fold: through cell membranes are ensured in many tissues by seleca NH 2 cytosolic portion followed by a hydrophobic stretch tive pores that belong to the major intrinsic protein family of six transmembrane helices ). Among highly (MIP). This family includes the water channels or aquaporins conserved amino acids in the family, two repetitions of (AQP) and the neutral solute facilitators such as the glycerol facilitator (GlpF). We have compared the characteristics of Asp, Pro, Ala residues (NPA box) localized in the B and representatives of each subfamily. Following solubilization in E loops draw the sequence signature of the family (Fig. the nondenaturing detergents n-octyl-glucoside (OG) and Tri-1B). The folding of these two loops in the membrane ton X-100 (T-X100), AQPs remain in their native homotetrabilayer is proposed to be responsible of the pore formameric state, while GlpF always behaves as a monomer. Solute facilitators are fully solubilized by the detergent N-lauroyl sartion and solute movement across the membrane [2, 3]. cosine (NLS), while AQPs are not. Analyses of mutants and Interestingly, AQPs are widely distributed in bacteria, chimeras demonstrate a close correlation between the water plants, and animals, while GlpFs have been characterized transport function and the resistance to NLS solubilization. only within microorganisms such as bacteria or yeast. In Thus, AQPs and solute facilitators exhibit different behaviors mammals, ten MIPs have been cloned and functionally in mild detergents; this could reflect differences in quaternary organization within the membranes. We propose that the oligocharacterized. Some of them, such as AQP1, AQP3, and merization state or the strength of self-association is part of the AQP4, are widely distributed in the body [4]. In contrast, mechanisms used by MIP proteins to ensure solute selectivity.