The plastoglobule-localized protein AtABC1K6 is a Mn 2+ -dependent kinase necessary for timely transition to reproductive growth

The Absence of bc Complex (ABC1) is an ancient, atypical protein kinase family that emerged prior to the archaeal-eubacterial divergence. Loss-of-function mutants in ABC1 genes are linked to respiratory defects in microbes and humans and to compromised photosynthetic performance and stress tolerance...

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Bibliographic Details
Published inThe Journal of biological chemistry Vol. 298; no. 4; p. 101762
Main Authors Espinoza-Corral, Roberto, Lundquist, Peter K
Format Journal Article
LanguageEnglish
Published United States 01.04.2022
Subjects
Arabidopsis - enzymology
Arabidopsis - genetics
Arabidopsis - growth & development
Arabidopsis Proteins - metabolism
Chloroplasts - metabolism
Mutation
Photosynthesis
Protein Kinases - genetics
Protein Kinases - metabolism
ABC1
kinase
ADCK
plastoglobule
COQ8
UbiB
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Summary:The Absence of bc Complex (ABC1) is an ancient, atypical protein kinase family that emerged prior to the archaeal-eubacterial divergence. Loss-of-function mutants in ABC1 genes are linked to respiratory defects in microbes and humans and to compromised photosynthetic performance and stress tolerance in plants. However, demonstration of protein kinase activity remains elusive, hampering their study. Here, we investigate a homolog from Arabidopsis thaliana, AtABC1K6, and demonstrate in vitro autophosphorylation activity, which we replicate with a human ABC1 ortholog. We also show that AtABC1K6 protein kinase activity requires an atypical buffer composition, including Mn as a divalent cation cofactor and a low salt concentration. AtABC1K6 associates with plastoglobule lipid droplets of A. thaliana chloroplasts, along with five paralogs. We show that the protein kinase activity associated with isolated A. thaliana plastoglobules was inhibited at higher salt concentrations, but could accommodate Mg as well as Mn , indicating salt sensitivity, but not the requirement for Mn , may be a general characteristic of ABC1 proteins. Finally, loss of functional AtABC1K6 impairs the developmental transition from vegetative to reproductive growth. This phenotype was complemented by the wild-type sequence of AtABC1K6, but not by a kinase-dead point mutant in the unique Ala-triad of the ATP-binding pocket, demonstrating the physiological relevance of the protein's kinase activity. We suggest that ABC1s are bona fide protein kinases with a unique regulatory mechanism. Our results open the door to detailed functional and mechanistic studies of ABC1 proteins and plastoglobules.
ISSN:1083-351X