Isolation of the cDNA for erythrocyte integral membrane protein of 28 kilodaltons: member of an ancient channel family.

Abstract

CHIP28 is a 28-kDa integral membrane protein with similarities to membrane chanch and Is found in erythrocytes and renal tubules. A cDNA for CHIP28 was isolated from human fetal liver cDNA template by a the-step polymerase chain reaction (PCR) Analysis of the deduced amino acid sequence sugss that CHEIP28 protein contains six bilayer-sannin domains, two exofacial potential N-glycosylation sites, and intraceflular N and C termini. Search of the DNA sequence data bas revealed a strong homology with the major intrinsic protein of bovine lens, which is the prototype of an ancient but recently recognized family of membrane channels. These proteins are believed to form channels permeable to water and possibly other small molecules. CHIP28 shares homology with all known members of this channel family, and it is speculated that CHIP28 has a similar function.The erythrocyte membrane has proven to be an accessible source of new proteins with structural or metabolic functions and a useful model with general relevance to plasma membranes (for reviews, see refs. 1 and 2). During isolation of the 32-kDa Rh polypeptides from human erythrocytes, a 28-kDa integral membrane protein copurified and was considered a breakdown product (3, 4). The 28-kDa protein was later shown to be a unique molecule that is abundant in erythrocytes and renal tubules, and a subpopulation is N-glycosy-The function of the 28-kDa protein is not yet known, but several observations suggest that it is a membrane channel. The 28-kDa protein behaves as a tetramer when solubilized in Triton X-100, and the N-terminal amino acid sequence of the purified 28-kDa protein (6) is related to that of MIP26, the 26-kDa major intrinsic protein of bovine lens fiber cells (7). When reconstituted into planar lipid bilayers, MIP26 forms tetrameric channels with voltage-regulated conductance (8,9), and MIP26 appears to function as a channel through which lens fiber cells absorb interstitial fluid (8). MMP26 is the prototype of a family of membrane proteins recently identified in diverse species (10). This report describes isolation of the cDNA* for the 28-kDa protein, which has homology with all known members of the MIP channel family and is referred to as

Reconstituted Aquaporin 1 Water Channels Transport CO2 across Membranes

“…The physiological relevance of this finding is not certain, but the abundance of AQP1 in tissues that serve to transport CO 2 such as red blood cells and in tissues that are intimately linked to bicarbonate-based pH control such as blood cells (21), renal proximal tubule (4), and choroid plexus (22) suggests that there may be an evolutionary advantage to rapid equilibration of CO 2 across these membranes. Studies of the permeabilities of other gases and studies in AQP1-deleted animals will provide further information about the physiological basis for this phenomenon.…”

The Aquaporins, Blueprints for Cellular Plumbing Systems

“…Sequence analysis suggested that AQP1 is a six-transmembrane domain integral protein (4). The N-and C-terminal halves of the protein are related sequences comprised of three bilayer spanning domains and connecting loops B and E, which each contain the signature motif Asn-Pro-Ala (Fig.…”

The Major Intrinsic Protein Family of Arabidopsis Has 23 Members That Form Three Distinct Groups with Functional Aquaporins in Each Group

“…Ec-CLPF (Weissenborn et al, 1992), Ec-AQPZ (Calamita et al, 1995), Cm-NOD26 (Fortin et a!., 1987), Os-rMIP1 (Liu et al, 1994), Na-U20490 (Newbigin, GenBank accession no. U20490), Hs-AQP1 (Preston and Agre, 1991), Hs-AQP2 (Deen et al, 1994), Hs-AQP3 (Ishibashi et al, 1995), Hs-AQP4 (Lu et al, 1996), and Hs-AQP5 .…”