Structural and functional studies of casein kinase I-like protein from rice

Exploration on cold adaptation of Antarctic lichen via detection of positive selection genes

Lichen as mutualistic symbiosis is the dominant organism in various extreme terrestrial environment on Earth, however, the mechanisms of their adaptation to extreme habitats have not been fully elucidated. In this study, we chose the Antarctic dominant lichen species Usnea aurantiacoatra to generate a high-quality genome, carried out phylogenetic analysis using maximum likelihood and identify genes under positive selection. We performed functional enrichment analysis on the positively selected genes (PSGs) and found that most of the PSGs focused on transmembrane transporter activity and vacuole components. This suggest that the genes related to energy storage and transport in Antarctic U. aurantiacoatra were affected by environmental pressure. Inside of the 86 PSGs screened, two protein interaction networks were identified, which were RNA helicase related proteins and regulator of G-protein signaling related proteins. The regulator of the G-protein signaling gene (UaRGS1) was chosen to perform further verification by the lichen genetic manipulation system Umbilicaria muhlenbergii. Given that the absence of UmRgs1 resulted in elevated lethality to cold shock, the role for UaRgs1 in Antarctic U. aurantiacoatra resistance to cold can be inferred. The investigation of lichen adaptation to extreme environments at the molecular level will be opened up.

Mut9p-LIKE KINASE Family Members: New Roles of the Plant-Specific Casein Kinase I in Plant Growth and Development

: Casein kinase I (CK1), a ubiquitous serine/threonine (Ser/Thr) protein kinase in eukaryotes, plays pivotal roles in a wide spectrum of cellular functions including metabolism, cell cycle progression, developmental control and stress responses. Plant CK1 evolves a lineage expansion, resulting in a unique branch of members exclusive to the kingdom. Among them, Arabidopsis Mut9p-LIKE KINASEs (MLKs) target diverse substrates including histones and the key regulatory proteins involving in physiological processes of light signaling, circadian rhythms, phytohormone and plant defense. Deregulation of the kinase activity by mutating the enzyme or the phosphorylation sites of substrates causes developmental disorders and susceptibility to adverse environmental conditions. MLKs have evolved as a general kinase that modifies transcription factors or primary regulatory proteins in a dynamic way. Here, we summarize the current knowledge of the roles of MLKs and MLK orthologs in several commercially important crops.

Molecular basis for blue light-dependent phosphorylation of Arabidopsis cryptochrome 2

Plant cryptochromes undergo blue light-dependent phosphorylation to regulate their activity and abundance, but the protein kinases that phosphorylate plant cryptochromes have remained unclear. Here we show that photoexcited Arabidopsis cryptochrome 2 (CRY2) is phosphorylated in vivo on as many as 24 different residues, including 7 major phosphoserines. We demonstrate that four closely related Photoregulatory Protein Kinases (previously referred to as MUT9-like kinases) interact with and phosphorylate photoexcited CRY2. Analyses of the ppk123 and ppk124 triple mutants and amiR^4k artificial microRNA-expressing lines demonstrate that PPKs catalyse blue light-dependent CRY2 phosphorylation to both activate and destabilize the photoreceptor. Phenotypic analyses of these mutant lines indicate that PPKs may have additional substrates, including those involved in the phytochrome signal transduction pathway. These results reveal a mechanism underlying the co-action of cryptochromes and phytochromes to coordinate plant growth and development in response to different wavelengths of solar radiation in nature.

Plant cryptochromes are regulated by blue-light dependent phosphorylation. Here the authors map the in vivo phosphorylation sites of Arabidopsis cryptochrome 2 and identify four closely related kinases that act to both activate and destabilize the receptor in response to blue light.

Structural dynamics of Casein Kinase I (CKI) from malarial parasite Plasmodium falciparum (Isolate 3D7): Insights from theoretical modelling and molecular simulations

The protein kinases (PKs), belonging to serine/threonine kinase (STKs), are important drug targets for a wide spectrum of diseases in human. Among protein kinases, the Casein Kinases (CKs) are vastly expanded in various organisms, where, the malarial parasite Plasmodium falciparum possesses a single member i.e., PfCKI, which can phosphorylate various proteins in parasite extracts in vitro condition. But, the structure-function relationship of PfCKI and dynamics of ATP binding is yet to be understood. Henceforth, an attempt was made to study the dynamics, stability, and ATP binding mechanisms of PfCKI through computational modelling, docking, molecular dynamics (MD) simulations, and MM/PBSA binding free energy estimation. Bi-lobed catalytic domain of PfCKI shares a high degree of secondary structure topology with CKI domains of rice, human, and mouse indicating co-evolution of these kinases. Molecular docking study revealed that ATP binds to the active site where the glycine-rich ATP-binding motif (G16-X-G18-X-X-G21) along with few conserved residues plays a crucial role maintaining stability of the complex. Structural superposition of PfCKI with close structural homologs depicted that the location and length of important loops are different, indicating the dynamic properties of these loops among CKIs, which is consistent with principal component analysis (PCA). PCA displayed that the overall global motion of ATP-bound form is comparatively higher than that of apo form. The present study provides insights into the structural features of PfCKI, which could contribute towards further understanding of related protein structures, dynamics of catalysis and phosphorylation mechanism in these important STKs from malarial parasite in near future.

Casein kinase I-like protein linked to lipase in plant

Casein kinase I (CKI) is a Ser/Thr kinase protein that is highly conserved from plants to animals. This enzyme is involved in various cellular functions, such as DNA repair, cell cycle, cytokinesis, vesicular trafficking, morphogenesis and circadian rhythm. The CKI family contains a highly conserved kinase domain at the N-terminus and a highly diverse regulatory domain at the C-terminus. The CKI-like protein has been indentified in rice and the 2.0 Å crystal structure of the kinase domain of the CKI-like protein from rice (riceCKI) was reported by our group recently. We also identified a lipase that was a substrate of riceCKI and showed that the activity of the lipase is controlled by the activity of riceCKI. Here, we identified potential phosphorylation sites on the lipase by molecular modeling and ser/thr mapping. Moreover, we showed that the activity of the lipase was decreased by CKI in a time-dependent manner.