Structure-function relationships in heparin cofactor II: chemical modification of arginine and tryptophan and demonstration of a two-domain structure

Suggestions on leading an academic research laboratory group

This commentary is about running an academic research laboratory group, including some reflections, memories, and tips on effectively managing such a group of scientists focused on one’s research. The author’s academic career has spanned from 1982 to 2022, including postdoctoral research associate through the rank of professor with tenure. Currently, the author is in the final year of 3 years of phased retirement. One must be willing to work hard at running a research laboratory. Also, stay focused on funding the laboratory tasks and publishing one’s work. Recruit the best people possible with advice from the collective laboratory group. Laboratory group members felt more like they were a part of a collective family than simply employees; however, what works best for the researcher is what matters. Several other points to discuss will include managing university roles, recruiting laboratory personnel, getting recognition, dealing with intellectual property rights, and publishing work. In closing, there are many more positives than negatives to leading a research laboratory group. Finally, one cannot replace the unforgettable memories and the legacy of a research laboratory group.

Designed polyanionic coiled-coil proteins: acceleration of heparin cofactor II inhibition of thrombin

Novel polyanionic proteins were designed to increase the rate of heparin cofactor II (HC) inhibition of alpha-thrombin, an essential protease in the coagulation cascade. Two alpha-helical coiled-coil proteins, a 62-residue dimer containing 8 Glu residues (E8C) and a 104-residue dimer containing 14 Glu residues (E14C), plus two 31-residue control peptides containing 8 Glu residues each (E8A and E8B), were chemically synthesized, structurally characterized and enzymatically assayed. Circular dichroic spectrophotometry indicated that both E8C and E14C formed stable two-chain alpha-helical coiled coils at pH 7 and 25 degrees C. The control peptides were only partially alpha-helical. E14C remained folded at 90 degrees C but E8C was half unfolded at 49 degrees C. Coiled-coil proteins E8C and E14C maximally accelerated by 35- and 33-fold, respectively, the rate of HC inhibition of alpha-thrombin. None of these compounds accelerated antithrombin inhibition of alpha-thrombin, and neither control peptide accelerated HC inhibition of alpha-thrombin. Acceleration of the HC inhibition of alpha-thrombin showed bimodal dependence on the concentration of the polyanionic protein, which is consistent with formation of a HC-coiled-coil-thrombin ternary complex. The results suggest that antithrombotic polyanionic alpha-helical coiled-coil proteins can be designed and synthesized and that the occurrence of secondary structure can be correlated with biological activity.

Immobilization of dermatan sulphate on a silica matrix and its possible use as an affinity chromatography support for heparin cofactor II purification

Dermatan sulphate (DS) is a glycosaminoglycan which catalyses specifically thrombin inhibition by a plasmatic inhibitor, Heparin cofactor II (HCII). DS was insolubilized on a silica matrix to study its interaction with HCII. The immobilization of DS was performed with a good yield on a silica previously coated with polysaccharides in order to neutralize the negatively charged silanol groups. The value of the affinity constant of insolubilized DS for HCII, measured by the adsorption isotherm, is consistent with the value obtained for soluble DS. The DS bound to the silica matrix was also tested as a chromatographic support for the purification of HCII from human plasma; the optimum conditions for HCII adsorption and desorption were determined. The eluted HCII was obtained with a good yield (21%) and with no contamination by antithrombin III, the other main plasmatic inhibitor of thrombin.

Binding of heparin or dermatan sulfate to thrombin is essential for the sulfated polysaccharide-accelerated inhibition of thrombin by heparin cofactor II

Heparin cofactor II (HC II) and thrombin were chemically modified with pyridoxal 5'-phosphate, and their effects on the inhibition of thrombin by HC II in the presence of heparin or dermatan sulfate were studied. The inhibition of thrombin by HC II was enhanced about 7000-fold in the presence of heparin or dermatan sulfate. However, this enhancement by heparin dwindled to 110- and 9.6-fold when the modified HC II and the modified thrombin, respectively, were substituted for native proteins. Essentially identical results were obtained from the experiments using dermatan sulfate. These results indicate that the binding of heparin or dermatan sulfate to both thrombin and HC II is required for the sulfated polysaccharide-dependent acceleration of the thrombin inhibition by HC II, and the binding to thrombin is more essential for the reaction.

Structure-function relationships in heparin cofactor II: spectral analysis of aromatic residues and absence of a role for sulfhydryl groups in thrombin inhibition

This study characterizes the structural and functional significance of sulfhydryl residues in human plasma heparin cofactor II (HCII). For quantification of sulfhydryl groups, the extinction coefficient of HCII was redetermined and found to be 0.593 ml mg-1 cm-1 using second-derivative spectroscopy and multicomponent analysis assuming 4, 10, and 2 residues of tryptophan, tyrosine, and tyrosine-O-sulfate per mole of protein, respectively. The results show that tyrosine-O-sulfate residues in HCII and in cholecystokinin peptide fragments (as model compounds) do not significantly contribute to the absorbance spectrum from 280 to 300 nm. A total of three sulfhydryl groups per mole of HCII was detected by Ellman's reagent titration, with or without treatment with dithioerythritol, indicating the absence of intramolecular disulfide bonds. Incubation of HCII with 0.1-10 mM dithioerythritol did not diminish its heparin-enhanced thrombin inhibition activity. Treatment with various sulfhydryl-specific reagents, including p-mercuribenzoate, HgCl2, and N-substituted maleimide derivatives, inactivated HCII. Titration with Ellman's reagent after these reactions identified the modification site as a cysteinyl residue(s). However, complete methanethio derivatization of the sulfhydryl groups of HCII using methyl methanethiosulfonate did not alter heparin-catalyzed thrombin inhibition. These results indicate that the sulfhydryl groups of HCII are not essential for thrombin inhibition. HCII differs from antithrombin III, which contains an essential disulfide bond for heparin-dependent thrombin inhibition (Longas, M. O., et al. (1980) J. Biol. Chem. 255, 3436). Furthermore, within the "serpin" (serine proteinase inhibitor) superfamily, HCII resembles chicken ovalbumin in occurrence of sulfhydryl residues and reactivity with various sulfhydryl group-directed compounds.

Carboxylate polyanions accelerate inhibition of thrombin by heparin cofactor II

The heparin cofactor II (HCII)/thrombin inhibition reaction is enhanced by various carboxylate polyanions. In the presence of polyaspartic acid, the HCII/thrombin reaction is accelerated more than 1000-fold with the second-order rate constant increasing from 3.2 x 10(4) M-1 min-1 (in the absence of polyAsp) to 3.6 x 10(7) M-1 min-1 as the polyAsp concentration is increased from 1 to 250 micrograms/ml. This accelerating effect was observed for HCII/thrombin, though to varying degrees, with other carboxylate polyanions. In contrast to HCII, the rate of antithrombin III inhibition of thrombin was decreased in the presence of polyAsp. The HCII/thrombin complex is rapidly formed in the presence of 10 micrograms/ml polyAsp when 125I-labeled-thrombin is incubated with plasma. It is possible that at physiological sites rich in carboxylate polyanions, thrombin may be preferentially inhibited by HCII.

Rapid sulfopropyl-disk chromatographic purification of bovine and human thrombin

Thrombin, from either a crude commercial preparation (bovine) or a prothrombin activation mixture (human), was purified by sulfopropyl-disk chromatography to homogeneity in a rapid and convenient single-step procedure. The yield of both proteinases was greater than 85%. Purified bovine and human thrombin had sp act of 2500 and 3000 "NIH" units/mg, respectively. Human thrombin was more reactive than bovine thrombin with these active site-directed probes: phenylmethylsulfonyl fluoride, dansyl-Glu-Gly-Arg-chloromethylketone, and human heparin cofactor II. The sulfopropyl-disk chromatographic method is a useful and rapid technique to prepare milligram quantities of highly purified bovine and human thrombin.