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Biomedical subjects

P S Chockalingam

Publications and source records attributed to P S Chockalingam.

4 recordsLinked to original sources
PubMed2001

DNA affinity chromatography.

DNA-affinity chromatography has been used for the purification of DNA-binding proteins that control various cellular processes. There have been improvements in coupling methods and choice of supports over the years. The procedure for coupling 5'-aminoethyl-(dT)18 to silica activated with N-hydroxysuccinimide and a carbodiimide has been described. Also, the cyanogen bromide mediated coupling of aminoethyl-(dT)18 to Sepharose is described. Determination of (dT)18-coupling to silica and Sepharose is by 5' end-labeling an oligonucleotide containing a (dA)18 stretch of sequence and determining how much hybridizes with the (dT)18 support. Enzymatic synthesis of a double-stranded DNA-silica or Sepharose prevents modification of nucleotide bases. We have explained the use of DNA and RNA templates for template-directed enzymatic synthesis of affinity columns. DNA-affinity chromatography is a powerful method with broad applicability and we are currently extending this technology for purifying transcription factors, polymerases, and nucleases.

Base Sequence↗
PubMed1999

Pleckstrin homology domain 1 of mouse alpha 1-syntrophin binds phosphatidylinositol 4,5-bisphosphate.

Mouse alpha 1-syntrophin sequences were produced as chimeric fusion proteins in bacteria and found to bind phosphatidylinositol 4, 5-bisphosphate (PtdIns4,5P2). Half-maximal binding occurred at 1.9 microM PtdIns4,5P2 and when 1.2 PtdIns4,5P2 were added per syntrophin. Binding was specific for PtdIns4,5P2 and did not occur with six other tested lipids including the similar phosphatidylinositol 4-phosphate. Binding was localized to the N-terminal pleckstrin homology domain (PH1); the second, C-terminal PH2 domain did not bind lipids. Key residues in PtdIns4,5P2 binding to a PH domain were found to be conserved in alpha-syntrophins' PH1 domains and absent in PH2 domains, suggesting a molecular basis for binding.

Amino Acid Sequence↗
PubMed1999

Apocalmodulin.

Intracellular Ca2+ is normally maintained at submicromolar levels but increases during many forms of cellular stimulation. This increased Ca2+ binds to receptor proteins such as calmodulin (CaM) and alters the cell's metabolism and physiology. Calcium-CaM binds to target proteins and alters their function in such a way as to transduce the Ca2+ signal. Calcium-free or apocalmodulin (ApoCaM) binds to other proteins and has other specific effects. Apocalmodulin has roles in the cell that apparently do not require the ability to bind Ca2+ at all, and these roles appear to be essential for life. Apocalmodulin differs from Ca2+-CaM in its tertiary structure. It binds target proteins differently, utilizing different binding motifs such as the IQ motif and noncontiguous binding sites. Other kinds of binding potentially await discovery. The ApoCaM-binding proteins are a diverse group of at least 15 proteins including enzymes, actin-binding proteins, as well as cytoskeletal and other membrane proteins, including receptors and ion channels. Much of the cellular CaM is bound in a Ca2+-independent manner to membrane structures within the cell, and the proportion bound changes with cell growth and density, suggesting it may be a storage form. Apocalmodulin remains tightly bound to other proteins as subunits and probably hastens the response of these proteins to Ca2+. The overall picture that emerges is that CaM cycles between its Ca2+-bound and Ca2+-free states and in each state binds to different proteins and performs essential functions. Although much of the research focus has been on the roles of Ca2+-CaM, the roles of ApoCaM are equally vital but less well understood.

Amino Acid Sequence↗