PIK3CA, one of the two most frequently mutated oncogenes in human tumors, codes for p110a, the catalytic subunit of a phosphatidylinositol 3-kinase, isoform a (PI3Ka, p110a/p85). Here, we report a 3.0 angstrom resolution structure of a complex between p110a and a polypeptide containing the p110a-binding domains of p85a, a protein required for its enzymatic activity. The structure shows that man...

DNA-dependent protein kinase (DNA-PK) is required for the repair of double-stranded DNA breaks through the nonhomologous DNA end joining pathway. DNA-PK activity is required for DNA repair, but kinase activity also appears to be attenuated through an autoregulatory feedback loop. We show that autophosphorylation of DNA-PK catalytic subunit occurs in trans at least three sites NH(2) terminal to ...

Acetohydroxyacid synthase (EC 4.1.3.18; AHAS) catalyzes the initial step in the formation of the branched-chain amino acids. The enzyme from most bacteria is composed of a catalytic subunit, and a smaller regulatory subunit that is required for full activity and for sensitivity to feedback regulation by valine. A similar arrangement was demonstrated recently for yeast AHAS, and a putative regul...

Ubiquitously expressed calpains are Ca(2+)-dependent, intracellular cysteine proteases comprising a large catalytic subunit (domains DI-DIV) and a noncovalently bound small regulatory subunit (domains DV and DVI). It is unclear whether Ca(2+)-induced calpain activation is followed by subunit dissociation or not. Here, we have applied advanced fluorescence microscopy techniques to study calpain ...

The phosphorylation of the calmodulin-dependent enzyme myosin light chain kinase, purified from bovine tracheal smooth muscle and human blood platelets, by the catalytic subunit of CAMP-dependent protein kinase and by cGMP-dependent protein kinase was investigated. When myosin light chain kinase which has calmodulin bound is phosphorylated by the catalytic subunit of CAMP-dependent protein kina...

The cAMP binding domain of the regulatory subunit (R) of Mucor rouxii protein kinase A was cloned. The deduced amino acid sequence was highly homologous in sequence and in size to the corresponding region in fungal and higher eukaryotic regulatory subunits (47-54%), but particularly homologous (62%) to Blastocladiella emersonii, a fungus classified in a different phylum. Amino acids reported to...

The cell-surface expression and function of multisubunit plasma membrane proteins are regulated via interactions between catalytic subunits and auxiliary subunits. Subunit assembly in the endoplasmic reticulum is required for the cell-surface expression of the enzyme, but little is known about subunit interactions once it reaches the plasma membrane. Here we performed highly quantitative analys...

Telomerase synthesizes chromosome-capping telomeric repeats using an active site in telomerase reverse transcriptase (TERT) and an integral RNA subunit template. The fundamental question of whether human telomerase catalytic activity requires cooperation across two TERT subunits remains under debate. In this study, we describe new approaches of subunit labeling for single-molecule imaging, appl...

Purified phosphofructokinase from the earthworm Lumbricus terrestris was phosphorylated in vitro by the catalytic subunit of cAMP-dependent protein kinase from the same organism to an extent of approx. 0.5 mol/mol of subunit. Activation of the enzyme occurred in parallel to the incorporation of covalently bound phosphate and was reversed by the action of the catalytic subunit of protein phospha...

Na+,K(+)-ATPase activity in nerve is reduced in rats with streptozotocin-induced diabetes; three different isoforms of the alpha (catalytic) subunit of the enzyme are present in nerve. Using western blot to determine subunit isoform polypeptide levels in sciatic nerve, we found a substantial reduction in alpha 1-isoform polypeptide (88% at 3 weeks, 94% at 8 weeks) after induction of diabetes by...