Klaus P. Hellmann

Studies on human porin: XIII. The type‐1 VDAC ‘Porin 31HL’ biotinylated at the plasmalemma of Trypan blue excluding human B lymphocytes

In 1989, we demonstrated for the first time the expression of the VDAC ‘Porin 31HL’ in the plasmalemma of human B lymphocytes, then giving first evidence of a multi‐topological expression of VDAC. Meanwhile, data from this and other laboratories support our proposal of a multi‐compartment distribution of the channel in mammalian tissues. Here, by biotinylation of plasmalemma‐integrated proteins of proven living B lymphocytes, followed by two‐dimensional electrophoresis, immuno‐ and streptavidin affinity blotting, we show that part of the channel molecules can be labelled at the outer membrane of the cells. Thus, by a relevant approach our results invalidate objections concerning putative cross‐reactivity of anti‐human Type‐1 porin antibodies with non‐VDAC proteins at the outer cell membrane.

Lineage- and differentiation-dependent alterations in the expression of receptors for glycoconjugates (lectins) in different human hematopoietic cell lines and low grade lymphomas

SummaryImportant biological functions and cellular recognition phenomena are supposedly governed by specific sugar-protein interactions. Human hematopoietic cell lines offer an excellent model for the study of the expression of endogenous receptors for the carbohydrate part of glycoconjugates with respect to cell lineage and modulation by differentiation. Initially, a panel of fluorescent (neo)glycoproteins was successfully employed to demonstrate cytologically the actual presence of such receptors on different cell lines: the B lymphoblast line, Daudi; the T cell lymphoblastic leukemia line, P 12; the multipotent leukemic line, K 562 and the promyelocytic line, HL 060. Biochemical analyses were performed using affinity chromatography on supports with immobilized lactose and asialofetuin (simple or complex β-galactosides), melibiose (α-galactoside), fucose, N-acetyl-D-galactosamine, maltose (α-glucoside), the mannose-rich yeast glycoprotein, mannan, glycopeptides containing sialic acid residues and heparin. Subsequently, sodium dodecyl sulfate-polyacrylamide slab gel electrophoresis was used to detect cell lineage-dependent changes in these parameters. Differentiation-dependent changes in the expression of receptors with specificity to galactose, N-acetylgalactosamine, maltose and heparin were similarly uncovered upon dimethyl sulfoxide-induced differentiation of HL 60 cells. Differences in this type of cellular characteristic were also apparent for lymphoma cells from patients with various histological subtypes of lowgrade lymphomas. This initial description of lineage- and differentiation-dependent differences in various human hematopoietic cell lines and in cells from patients with lowgrade lymphomas suggests that advances in the knowledge of the composition of endogenous sugar receptors (lectins) may aid in understanding aspects of the biological behavior of hematopoietic cells and their related malignancies via participation of sugar-protein (lectin) interactions.

Identification of a cell cycle-dependent gene product as a sialic acid-binding protein

A Ca2+-dependent sialic acid-binding protein was purified on fetuin-Sepharose from various types of human tissue. The molecular mass was determined to be 10,315 Da by laser desorption mass spectrometry. Partial sequence analysis after cyanogen bromide cleavage that yielded one N-terminus accessible for Edman degradation revealed an identity to an internal stretch following the only methionine residue within a putative amino acid sequence (Mr 10,048), deduced from the cDNA of a cell cycle-specific gene. The reported biochemical identification is a prerequisite to infer the biological role of the so far undetected gene product. Initial glycohistochemical studies with sialic acid-(BSA-biotin) raised evidence for nuclear localization of sialic acid-binding sites that might reflect, at least in part, detection of this protein.

LENTIL LECTIN ENRICHED MICROSOMES FROM THE PLASMA MEMBRANE OF THE HUMAN B-LYMPHOCYTE CELL LINE H2LCL CARRY A HEAVY LOAD OF TYPE-1 PORIN

Using an established biochemical approach, five subcellular fractions of human B lymphocytes were prepared by differential centrifugation. Crude membranes were passed over a lentil lectin column to enrich carbohydrate-coated cell surface microsomes. The lectin-bound fraction contained a high amount of plasma membrane-derived microsomes as indicated by cell surface markers. All subcellular fractions in Western blots proved to contain distinct but variable amounts of porin. There was a strong increase in porin content from crude membranes to plasma membrane-derived vesicles. The porin content of this fraction appeared to be higher than that of mitochondria. In the final step the plasma membrane-derived microsome fraction proved to be devoid of contamination by outer mitochondrial membranes, as revealed by antibodies against the established markers MAO B and Tom20 applied in Western blots. These data prove the extramitochondrial expression of human type-1 porin/ type-1 VDAC.

Carrier-immobilized derivatized lysoganglioside GM1 is a ligand for specific binding sites in various human tumor cell types and peripheral blood lymphocytes and monocytes

Biotinylation of ganglioside-protein conjugates, derived from selective N-acylation of the sphingoid amino group of deacylated ganglioside GM1 or a ganglioside mixture, yielded probes to detect specific binding sites in fixed specimens. GM1-containing neoligandoprotein significantly bound to tumor cells in sections of 15 out of 16 cases of human lung cancer, while the probe, derived from the mixture, was ineffective under these conditions. The same graduation of staining was under identical conditions observed with these two probes on fixed human tumor cells and on peripheral blood lymphocytes and monocytes. Attempts of biochemical isolation of proteins, responsible for this binding capacity, from tumor cell extracts in the presence of the abundant endogenous ligands led to protein bands with apparent molecular weights of 44,000, 68,000 and 72,000 with yields of 0.1-0.24 micrograms/mg protein, after the detergent extracts had been passed over a resin, exposing gangliosides of the markedly less efficient mixture, to exclude binding by non-specific ionic or hydrophobic interactions.

Preparation of neoglycoprotein-enzyme conjugate using a heterobifunctional reagent and its use in solid-phase assays and histochemistry

A conjugate of a neoglycoprotein (chemically lactosylated bovine serum albumin) and an enzyme (horseradish peroxidase) has been prepared in solution using a heterobifunctional reagent, N-succinimidyl-3-(2-pyridyldithio)propionate, and has been purified by gel filtration on an Ultrogel AcA-44 column. To preclude any carbohydrate-dependent binding to the sugar residues on the glycoprotein peroxidase, the enzyme has to be treated with sodium periodate and sodium cyanoborohydride prior to coupling, which results in oxidative cleavage of the carbohydrates and reduction of the aldehydes thus formed to primary alcohols. Lactosylated bovine serum albumin-peroxidase conjugate has been employed to detect plastic-bound Ricinus communis agglutinin with dependence of the concentration of the lectin and with dependence of the presence of specific inhibitors. Enzyme-labeled conjugates with unmodified bovine serum albumin are completely ineffective in this assay. Localization of beta-galactoside-specific sugar receptors in connective tissue is used to demonstrate the feasibility of application of such neoglycoprotein-enzyme conjugates in histochemistry with a minimum number of steps.

Endogenous sugar receptor pattern in human glioblastomas and gangliocytomas studied by histochemical application of biotinylated (neo)glycoproteins and affinity chromatography

SummaryBiotinylation of chemically glycosylated bovine serum albumin, yielding a panel of neoglycoproteins, and of desialylated, naturally occurring glycoproteins allowed to systematically evaluate presence and distribution of various types of endogenous sugar receptors in the sections of human glioblastomas and gangliocytomas by a routine histochemical procedure. Pronounced cytoplasmic staining with markers, carrying constituents of natural glycoconjugates, e.g. for β-galactoside-specific receptors, contrasted with the different intensities, noticed for α- and β-glucosidespecific receptors. Significant qualitative differences between the two tumor types were detected with N-acetyl-D-galactosamine-and sialic acid-carrying probes. Nuclear staining with only a part of the applied panel underscored the specificity of the protein-carbohydrate interaction. Fine structural features of the synthetic neoglycoproteins, e.g. the mode of coupling of the carbohydrate moiety to the protein, were found to exert a significant influence on their suitability as histochemical markers. On the basis of the histochemical results, exemplary biochemical analysis of certain classes of endogenous sugar receptors by affinity chromatography and subsequent gel electrophoresis, namely of β-galactoside-, α-fucoside-, α-mannoside- and α-glucoside-specific proteins, revealed presence and characteristics of respective sugar receptors that can contribute to the histochemical staining. Similar extent of histochemical staining with the respective probes notwithstanding, the different tumor types exhibited qualitative differences in the expression of individual endogenous sugar receptors. The combined histochemical and biochemical analysis is supposed to be of conspicuous value for biological and clinical investigations on endogenous sugar receptors.