Heterotetrameric Composition of Aquaporin-4 Water Channels
详细信息 查看全文
- 作者：John D. Neely ; Birgitte M. Christensen ; S
//pubs.acs.org/images/gifchars/oslash.gif" border="0">ren Nielsen ; and Peter Agre
- 刊名：Biochemistry
- 出版年：1999
- 出版时间：August 24, 1999
- 年：1999
- 卷：38
- 期：34
- 页码：11156 - 11163
- 全文大小：103K
- 年卷期：v.38,no.34(August 24, 1999)
- ISSN：1520-4995
文摘
Aquaporin (AQP) water channel proteins are tetrameric assemblies of individually active ~30kDa subunits. AQP4 is the predominant water channel protein in brain, but immunoblotting of nativetissues has previously yielded multiple poorly resolved bands. AQP4 is known to encode two distinctmRNAs with different translation initiating methionines, M1 or M23. Using SDS-PAGE urea gels andimmunoblotting with anti-peptide antibodies, four polypeptides were identified in brain and multiple otherrat tissues with the following levels of expression: 32 kDa > 34 kDa > 36 kDa > 38 kDa. The 34 and38 kDa polypeptides react with an antibody specific for the N-terminus of the M1 isoform, and 32 and36 kDa correspond to the shorter M23 isoform. Immunogold electron microscopic studies with ratcerebellum cryosections demonstrated that the 34 kDa polypeptide colocalizes in perivascular astrocyteendfeet where the 32 kDa polypeptide is abundantly expressed. Velocity sedimentation, cross-linking,and immunoprecipitation analyses of detergent-solubilized rat brain revealed that the 32 and 34 kDapolypeptides reside within heterotetramers. Immunoprecipitation of AQP4 expressed in Xenopus laevisoocytes demonstrated that heterotetramer formation reflects the relative expression levels of the 32 and34 kDa polypeptides; however, tetramers containing different compositions of the two polypeptides exhibitsimilar water permeabilities. These studies demonstrate that AQP4 heterotetramers are formed from twooverlapping polypeptides and indicate that the 22-amino acid sequence at the N-terminus of the 34 kDapolypeptide does not influence water permeability but may contribute to membrane trafficking or assemblyof arrays.