期刊
INTERNATIONAL JOURNAL OF MOLECULAR SCIENCES
卷 22, 期 24, 页码 -出版社
MDPI
DOI: 10.3390/ijms222413556
关键词
syntaxin; CK2 phosphorylation; PC12 cells; exocytosis; amperometry; FRET; evoked release
资金
- Israel Academy of Sciences [1623/21]
In this study, we found that the polybasic juxtamembrane region of syntaxin1A acts as a fusion clamp in PC12 cells and is required for depolarization-induced Ca2+-dependent opening of Syx. Phosphorylation of Syx at Ser-14 by casein kinase 2 was identified as a key molecular determinant for this process. The S14 phosphorylation confers the requirement for the close-to-open transition of Syx, which is crucial for both Ca2+-triggered release and spontaneous release.
The polybasic juxtamembrane region (5RK) of the plasma membrane neuronal SNARE, syntaxin1A (Syx), was previously shown by us to act as a fusion clamp in PC12 cells, as charge neutralization of 5RK promotes spontaneous and inhibits Ca2+-triggered release. Using a Syx-based FRET probe (CSYS), we demonstrated that 5RK is required for a depolarization-induced Ca+2-dependent opening (close-to-open transition; CDO) of Syx, which involves the vesicular SNARE synaptobrevin2 and occurs concomitantly with Ca2+-triggered release. Here, we investigated the mechanism underlying the CDO requirement for 5RK and identified phosphorylation of Syx at Ser-14 (S14) by casein kinase 2 (CK2) as a crucial molecular determinant. Thus, following biochemical verification that both endogenous Syx and CSYS are constitutively S14 phosphorylated in PC12 cells, dynamic FRET analysis of phospho-null and phospho-mimetic mutants of CSYS and the use of a CK2 inhibitor revealed that the S14 phosphorylation confers the CDO requirement for 5RK. In accord, amperometric analysis of catecholamine release revealed that the phospho-null mutant does not support Ca2+-triggered release. These results identify a functionally important CK2 phosphorylation of Syx that is required for the 5RK-regulation of CDO and for concomitant Ca2+-triggered release. Further, also spontaneous release, conferred by charge neutralization of 5RK, was abolished in the phospho-null mutant.
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