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A role for the carbohydrate‐binding module ( CBM ) in regulatory Sn RK 1 subunits: the effect of maltose on Sn RK 1 activity
Author(s) -
RuizGayosso Ana,
RodríguezSotres Rogelio,
MartínezBarajas Eleazar,
Coello Patricia
Publication year - 2018
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.14026
Subject(s) - protein subunit , maltose , biochemistry , maltose binding protein , chemistry , arabidopsis , recombinant dna , biology , microbiology and biotechnology , mutant , enzyme , gene , fusion protein
Summary Sn RK 1 is a protein kinase complex that is involved in several aspects of plant growth and development. There are published data indicative of a participation of Sn RK 1 in the regulation of the synthesis and degradation of starch, although the molecular mechanism is not known. In this work, we performed electron microscopy to explore the in vivo localization of the regulatory and catalytic subunits that constitute the Sn RK 1 complex. The results indicated that all the subunits are present in the chloroplast and, in particular, the Sn RK 1 βγ and Sn RK 1 β3 subunits are associated with starch. Furthermore, the regulatory subunits bind maltose, a relevant product of starch degradation. The kinase activity of immunoprecipitated complexes containing the βγ regulatory subunit was positively regulated by maltose only in the complexes obtained from Arabidopsis leaves collected at dusk. Recombinant complexes with the Sn RK 1α1 catalytic subunit, Sn RK 1βγ and three different β subunits showed that maltose only had an effect on a complex formed with the β3 subunit. Truncation of the CBM domain form Sn RK 1 βγ abolished the maltose activation of the complex and the activity was significantly reduced, indicating that the CBM is a positive regulator of Sn RK 1. A model of the Sn RK 1α1/βγ/β3 complex suggests the presence of two putative maltose‐binding sites, both involving ligand interactions with the βγ subunit and the α subunit.