Biomedical subjects

Malini Seth

Publications and source records attributed to Malini Seth.

4 recordsLinked to original sources

PubMed2006

Bap31 enhances the endoplasmic reticulum export and quality control of human class I MHC molecules.

The assembly of class I MHC molecules and their export from the endoplasmic reticulum (ER) is governed by chaperones and accessory proteins. We present evidence that the putative cargo receptor protein Bap31 participates in the transport and the quality control of human class I molecules. Transfection of the human adenocarcinoma cell line HeLa with yellow fluorescent protein-Bap31 chimeras increased surface levels of class I in a dose-dependent manner, by as much as 3.7-fold. The increase in surface class I resulted from an increase in the rate of export of newly synthesized class I molecules to the cell surface and from an increase in the stability of the exported molecules. We propose that Bap31 performs quality control on class I molecules in two distinct phases: first, by exporting peptide-loaded class I molecules to the ER/Golgi intermediate compartment, and second, by retrieving class I molecules that have lost peptides in the acidic post-ER environment. This function of Bap31 is conditional or redundant, because we find that Bap31 deficiency does not reduce surface class I levels. Overexpression of the Bap31 homolog, Bap29, decreases surface class levels in HeLa, indicating that it does not substitute for Bap31.

Bacterial Proteins↗

PubMed2005

Studies of Ca2+ ATPase (SERCA) inhibition.

The Ca(2+) transport ATPase of intracellular membranes (SERCA) can be inhibited by a series of chemical compounds such as Thapsigargin (TG), 2,5-di(tert-butyl)hydroquinone (DBHQ) and 1,3-dibromo-2,4,6-tris (methyl-isothio-uronium) benzene (Br(2)-TITU). These compounds have specific binding sites in the ATPase protein, and different mechanisms of inhibition. On the other hand, SERCA gene silencing offers a convenient and specific method for suppression of SERCA activity in cells. The physiological and pharmacological implications of SERCA inhibition are discussed.

Binding Sites↗

PubMed2003

Dependence of exogenous SERCA gene expression on coxsackie adenovirus receptor levels in neonatal and adult cardiac myocytes.

We demonstrate that the efficiency of adenovirus-assisted exogenous Ca(2+) ATPase (SERCA) and reporter (EGFP) gene expression is much higher in primary cultures of myocytes from neonatal rat hearts, than in primary cultures of myocytes from adult rat hearts. In this respect, the neonatal myocytes behave similarly to the established COS-1 cell line. This difference is related to the level of coxsackie adenovirus receptor (CAR) that affects cell penetration and expression level of exogenous genes, and explains variations in the observed consequences of exposure to adenovirus vector carrying SERCA cDNA. Awareness of these differences should be highly advantageous in complementary studies of exogenous gene expression in neonatal and adult myocytes. It should also be advantageous in evaluating conditions yielding optimal ratios of functional benefits over possible toxic effects upon exogenous SERCA gene delivery to cardiac muscle.

Adult↗

PubMed2002

Poly(C) synthesis by class I and class II CCA-adding enzymes.

The CCA-adding enzymes [ATP(CTP):tRNA nucleotidyl transferases], which catalyze synthesis of the conserved CCA sequence to the tRNA 3' end, are divided into two classes. Recent studies show that the class II Escherichia coli CCA-adding enzyme synthesizes poly(C) when incubated with CTP alone, but switches to synthesize CCA when incubated with both CTP and ATP. Because the poly(C) activity can shed important light on the mechanism of the untemplated synthesis of CCA, it is important to determine if this activity is also present in the class I CCA enzymes, which differ from the class II enzymes by significant sequence divergence. We show here that two members of the class I family, the archaeal Sulfolobus shibatae and Methanococcus jannaschii CCA-adding enzymes, are also capable of poly(C) synthesis. These two class I enzymes catalyze poly(C) synthesis and display a response of kinetic parameters to the presence of ATP similar to that of the class II E. coli enzyme. Thus, despite extensive sequence diversification, members of both classes employ common strategies of nucleotide addition, suggesting conservation of a mechanism in the development of specificity for CCA. For the E. coli enzyme, discrimination of poly(C) from CCA synthesis in the intact tRNA and in the acceptor-TPsiC domain is achieved by the same kinetic strategy, and a mutation that preferentially affects addition of A76 but not poly(C) has been identified. Additionally, we show that enzymes of both classes exhibit a processing activity that removes nucleotides in the 3' to 5' direction to as far as position 74.

Adenosine Triphosphate↗