4ae9 | pdb_00004ae9
A Crystal Structure of the Sperm Specific Isoform of Protein Kinase A (PKA) Subunit CalphaS Reveals a Binding Pocket for Hydrophobic Moieties
Structural highlights
Function[KAPCA_HUMAN] Phosphorylates a large number of substrates in the cytoplasm and the nucleus. Regulates the abundance of compartmentalized pools of its regulatory subunits through phosphorylation of PJA2 which binds and ubiquitinates these subunits, leading to their subsequent proteolysis. Phosphorylates CDC25B, ABL1, NFKB1, CLDN3, PSMC5/RPT6, PJA2, RYR2, RORA, TRPC1 and VASP. RORA is activated by phosphorylation. Required for glucose-mediated adipogenic differentiation increase and osteogenic differentiation inhibition from osteoblasts. Involved in the regulation of platelets in response to thrombin and collagen; maintains circulating platelets in a resting state by phosphorylating proteins in numerous platelet inhibitory pathways when in complex with NF-kappa-B (NFKB1 and NFKB2) and I-kappa-B-alpha (NFKBIA), but thrombin and collagen disrupt these complexes and free active PRKACA stimulates platelets and leads to platelet aggregation by phosphorylating VASP. Prevents the antiproliferative and anti-invasive effects of alpha-difluoromethylornithine in breast cancer cells when activated. RYR2 channel activity is potentiated by phosphorylation in presence of luminal Ca(2+), leading to reduced amplitude and increased frequency of store overload-induced Ca(2+) release (SOICR) characterized by an increased rate of Ca(2+) release and propagation velocity of spontaneous Ca(2+) waves, despite reduced wave amplitude and resting cytosolic Ca(2+). TRPC1 activation by phosphorylation promotes Ca(2+) influx, essential for the increase in permeability induced by thrombin in confluent endothelial monolayers. PSMC5/RPT6 activation by phosphorylation stimulates proteasome. Regulates negatively tight junction (TJs) in ovarian cancer cells via CLDN3 phosphorylation. NFKB1 phosphorylation promotes NF-kappa-B p50-p50 DNA binding. Involved in embryonic development by down-regulating the Hedgehog (Hh) signaling pathway that determines embryo pattern formation and morphogenesis. Isoform 2 phosphorylates and activates ABL1 in sperm flagellum to promote spermatozoa capacitation. Prevents meiosis resumption in prophase-arrested oocytes via CDC25B inactivation by phosphorylation. May also regulate rapid eye movement (REM) sleep in the pedunculopontine tegmental (PPT). Phosphorylates APOBEC3G and AICDA.[1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] Publication Abstract from PubMedProtein kinase A (PKA) exists as several tissue-specific isoforms that through phosphorylation of serine and threonine residues of substrate proteins act as key regulators of a number of cellular processes. We here demonstrate that the human sperm-specific isoform of PKA named Calpha2 is important for sperm motility and thus male fertility. Furthermore, we report on the first three-dimensional crystal structure of human apo Calpha2 to 2.1 A. Apo Calpha2 displays an open conformation similar to the well-characterized apo structure of murine Calpha1. The asymmetric unit contains two molecules and the core of the small lobe is rotated by almost 13 degrees in the A molecule relative to the B molecule. In addition, a salt bridge between Lys72 and Glu91 was observed for Calpha2 in the apo-form, a conformation previously found only in dimeric or ternary complexes of Calpha1. Human Calpha2 and Calpha1 share primary structure with the exception of the amino acids at the N-terminus coded for by an alternative exon 1. The N-terminal glycine of Calpha1 is myristoylated and this aliphatic chain anchors the N-terminus to an intramolecular hydrophobic pocket. Calpha2 cannot be myristoylated and the crystal structure revealed that the equivalent hydrophobic pocket is unoccupied and exposed. Nuclear magnetic resonance (NMR) spectroscopy further demonstrated that detergents with hydrophobic moieties of different lengths can bind deep into this uncovered pocket. Our findings indicate that Calpha2 through the hydrophobic pocket has the ability to bind intracellular targets in the sperm cell, which may modulate protein stability, activity and/or cellular localization. Structure and function of the human sperm-specific isoform of protein kinase A (PKA) catalytic subunit Calpha2.,Hereng TH, Backe PH, Kahmann J, Scheich C, Bjoras M, Skalhegg BS, Rosendal KR J Struct Biol. 2012 Jun;178(3):300-10. doi: 10.1016/j.jsb.2012.03.013. Epub 2012 , Apr 6. PMID:22504716[12] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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