Differential expression of a C-terminal splice variant of phosphatidylinositol transfer protein β lacking the constitutive-phosphorylated Ser262 that localizes to the Golgi compartment
Differential expression of a C-terminal splice variant of phosphatidylinositol transfer protein β lacking the constitutive-phosphorylated Ser262 that localizes to the Golgi compartment
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DOI：
10.1042/bj20060420
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发表时间：
2006-09-15
影响因子：
4.1
通讯作者：
Cockcroft, Shamshad
中科院分区：
文献类型：
--
作者：
Morgan, Clive P.;Allen-Baume, Victoria;Cockcroft, Shamshad
哺乳动物PITPβ(磷脂酰肌醇转移蛋白)是一种由272个氨基酸组成的多肽，能够在膜双层之间转运PtdIns、PtdCho和SM(鞘磷脂)。据报道，PITPβC末端的Ser(262)是结构性磷酸化的，决定高尔基体的定位。我们为PITP的一个SP(剪接)变异体(PITPβ-sp2)的表达提供了证据，其中PITPβ-SP1的C端15个氨基酸被16个氨基酸的替代C端取代。PITPβ-SP1是前11个外显子的产物，而PITPβ-SP2是前10个外显子的产物，紧随其后的是第12个外显子-外显子11被跳过。两种剪接变异体都能转运PtdIns和PtdCho，而PITPβ-sp2不能转运SM。PITPβ广泛表达，在HL60细胞和大鼠肝脏中PITPβ含量最高；HL60细胞只表达PITPβ-SP1，而大鼠肝脏表达两种SP变异体。在这两种类型的细胞中，PITPβ-SP1被结构性磷酸化，PtdIns和PtdCho形式的PITPβ-SP1都存在。相反，PITPβ-sp2缺乏组成磷酸化的丝氨酸(262)(被谷氨酰胺取代)。尽管如此，两个PITPβ变异体都定位于高尔基体，而且，PITPβ-SP1的Ser(262)去磷酸化不影响其高尔基体定位。PITPβSP变异体的存在增加了额外水平的蛋白质组复杂性，在大鼠肝脏中，PITPβ的单一基因产生了七种不同的蛋白质种类，可以根据它们的电荷差异进行解析。
Mammalian PITP beta (phosphatidylinositol transfer protein) is a 272-amino-acid polypeptide capable of transferring PtdIns, PtdCho and SM (sphingomyelin) between membrane bilayers. It has been reported that Ser(262) present in the C-terminus of PITP beta is constitutively phosphorylated and determines Golgi localization. We provide evidence for the expression of an sp (splice) variant of PITP (PITP beta-sp2) where the C-terminal 15 amino acids of PITP beta-sp1 are replaced by an alternative C-terminus of 16 amino acids. PITP beta-sp1 is the product of the first 11 exons, whereas PITP beta-sp2 is a product of the first 10 exons followed by the twelfth exon - exon 11 being 'skipped'. Both splice variants are capable of PtdIns and PtdCho transfer, with PITP beta-sp2 being unable to transport SM. PITP beta is ubiquitously expressed, with the highest amounts of PITP beta found in HL60 cells and in rat liver; HL60 cells express only PITP beta-sp1, whereas rat liver expresses both sp variants in similar amounts. In both cell types, PITP beta-sp1 is constitutively phosphorylated and both the PtdIns and PtdCho forms of PITP beta-sp1 are present. In contrast, PITP beta-sp2 lacks the constitutively phosphorylated Ser(262) (replaced with glutamine). Nonetheless, both PITP beta variants localize to the Golgi and, moreover, dephosphorylation of Ser(262) of PITP beta-sp1 does not affect its Golgi localization. The presence of PITP beta sp variants adds an extra level of proteome complexity and, in rat liver, the single gene for PITP beta gives rise to seven distinct protein species that can be resolved on the basis of their charge differences.