Deb K. Barma

Requirement of inositol pyrophosphates for full exocytotic capacity in pancreatic β cells

Inositol pyrophosphates are recognized components of cellular processes that regulate vesicle trafficking, telomere length, and apoptosis. We observed that pancreatic β cells maintain high basal concentrations of the pyrophosphate diphosphoinositol pentakisphosphate (InsP7 or IP7). Inositol hexakisphosphate kinases (IP6Ks) that can generate IP7 were overexpressed. This overexpression stimulated exocytosis of insulin-containing granules from the readily releasable pool. Exogenously applied IP7 dose-dependently enhanced exocytosis at physiological concentrations. We determined that IP6K1 and IP6K2 were present in β cells. RNA silencing of IP6K1, but not IP6K2, inhibited exocytosis, which suggests that IP6K1 is the critical endogenous kinase. Maintenance of high concentrations of IP7 in the pancreatic β cell may enhance the immediate exocytotic capacity and consequently allow rapid adjustment of insulin secretion in response to increased demand.

Structural Analysis and Detection of Biological Inositol Pyrophosphates Reveal That the Family of VIP/Diphosphoinositol Pentakisphosphate Kinases Are 1/3-Kinases

We have characterized the positional specificity of the mammalian and yeast VIP/diphosphoinositol pentakisphosphate kinase (PPIP5K) family of inositol phosphate kinases. We deployed a microscale metal dye detection protocol coupled to a high performance liquid chromatography system that was calibrated with synthetic and biologically synthesized standards of inositol pyrophosphates. In addition, we have directly analyzed the structures of biological inositol pyrophosphates using two-dimensional 1H-1H and 1H-31P nuclear magnetic resonance spectroscopy. Using these tools, we have determined that the mammalian and yeast VIP/PPIP5K family phosphorylates the 1/3-position of the inositol ring in vitro and in vivo. For example, the VIP/PPIP5K enzymes convert inositol hexakisphosphate to 1/3-diphosphoinositol pentakisphosphate. The latter compound has not previously been identified in any organism. We have also unequivocally determined that 1/3,5-(PP)2-IP4 is the isomeric structure of the bis-diphosphoinositol tetrakisphosphate that is synthesized by yeasts and mammals, through a collaboration between the inositol hexakisphosphate kinase and VIP/PPIP5K enzymes. These data uncover phylogenetic variability within the crown taxa in the structures of inositol pyrophosphates. For example, in the Dictyostelids, the major bis-diphosphoinositol tetrakisphosphate is 5,6-(PP)2-IP4 ( Laussmann, T., Eujen, R., Weisshuhn, C. M., Thiel, U., Falck, J. R., and Vogel, G. (1996) Biochem. J. 315, 715-725 ). Our study brings us closer to the goal of understanding the structure/function relationships that control specificity in the synthesis and biological actions of inositol pyrophosphates.

Regioselective de-O-benzylation of monosaccharides

Abstract Poly- O -benzylated sugars are regioselectively debenzylated using CrCl 2 /LiI in moist EtOAc. A predictive, three-point coordination model is proposed.

Inhibition of telomerase by BIBR 1532 and related analogues.

BIBR 1532 has been reported to be a potent, small molecule inhibitor of human telomerase, suggesting it as a lead for the development of anti-telomerase therapy. We confirm the ability of BIBR 1532 to inhibit telomerase and report the discovery of an equally potent analogue. Importantly, IC(50) values in cell extract are considerably higher than those previously reported using assays for purified enzyme, indicating that substantial improvement may be necessary.

A convenient synthesis of (Z)-1-chloro-1-alkenes and (Z)-1-chloro-2-alkoxy-1-alkenes

Abstract Mild, room temperature CrCl 2 reduction of 1,1,1-trichloroalkanes stereoselectively generates ( Z )-1-chloro-2-substituted-1-alkenes in excellent yields.

A versatile synthesis of 2-haloalk-2(Z)-en-1-ols and 1-chloro-1(Z)-alkenes from trichloromethylcarbinols

Abstract— CrCl 2 converts trichloromethylcarbinols under mild conditions to ( E )- -haloalkylidene chromium carbenoids whichadd to aldehydes or are quenched with water affording 2-haloalk-2( Z )-en-1-ols and 1-chloro-1( Z )-alkenes, respectively, in highyield.

α-chlorovinylation: Synthesis of 2-chloropropenyl and propargyl alcohols

Abstract Formal α-chlorovinylation of aldehydes using CH 3 CCl 3 CrCl 2 affords 2-chloropropenyl alcohols from which terminal propargyl alcohols are obtained via base induced elimination.

Three-component synthesis of 2-haloalk-2(Z)-en-1-ols via tandem haloalkylidenation–aldehyde addition

Abstract Cr(II)-induced condensation of CCl 4 or CBr 4 with an aldehyde stereospecifically generates an ( E )-α-haloalkylidene chromium carbenoid which adds in situ to a second equivalent of aldehyde furnishing 2-haloalk-2( Z )-en-1-ols in high yield.

Cascade Synthesis of (E)-2-Alkylidenecyclobutanols

A facile, one-pot reaction cascade condenses 1,1,1-trichloroalkanes with alpha,beta-unsaturated ketones to unexpectedly furnish moderate to good yields of (E)-2-alkylidenecyclobutanols.

A tagging-via-substrate technology for genome-wide detection and identification of farnesylated proteins.

Protein farnesylation is one of the most common lipid modifications and has an important role in the regulation of various cellular functions. We have recently developed a novel proteomics strategy, designated the tagging-via-substrate (TAS) approach, for the detection and proteomic analysis of farnesylated proteins. This chapter describes the principle of TAS technology and details the method for detection and enrichment of farnesylated proteins.