The major integral proteins of spinach leaf plasma membranes are putative aquaporins and are phosphorylated in response to Ca2+ and apoplastic water potential

被引:260
作者
Johansson, I
Larsson, C
Ek, B
Kjellbom, P
机构
[1] LUND UNIV,DEPT PLANT BIOCHEM,S-22100 LUND,SWEDEN
[2] SWEDISH UNIV AGR SCI,UPPSALA GENET CTR,DEPT CELL RES,S-75007 UPPSALA,SWEDEN
关键词
D O I
10.1105/tpc.8.7.1181
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
We show that homologs of the major intrinsic protein (MIP) family are major integral proteins of the spinach leaf plasma membrane and constitute similar to 20% of integral plasma membrane protein, By using oligonucleotide primers based on partial amino acid sequences for polymerase chain reaction and screening of a spinach leaf cDNA library, we obtained two full-length clones of MIP homologs (pm28a and pm28b). One of these clones, pm28a, was sequenced, and it encodes a protein (PM28A) of 281 amino acids with a molecular mass of 29.9 kD. DNA gel blots indicated that PM28A is the product of a single gene, and RNA gel blots showed that pm28a is ubiquitously expressed in the plant. In vivo phosphorylation of the 28-kD polypeptide(s), corresponding to PM28A and PM28B, was dependent on apoplastic water potential, suggesting a role in regulation of cell turgor for these putative aquaporins. In vitro, only one of the homologs, PM28A, was phosphorylated, Phosphorylation of PM28A occurred on Ser-274, seven amino acids from the C terminus of the protein, within a consensus phosphorylation site (Ser-X-Arg) for vertebrate protein kinase C, In vitro phosphorylation of PM28A was due to a plasma membrane-associated protein kinase and was strictly dependent on submicromolar concentrations of Ca2+.
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页码:1181 / 1191
页数:11
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