The primary structures of N-terminal 19-mer peptides, released by limited trypsin treatment of coat protein (CP) subunits in intact virions of three potato virus X (PVX) isolates, were analyzed. Two wild-type PVX strains, Russian (Ru) and British (UK3), were used and also the ST mutant of UK3 in which all 12 serine and threonine residues in the CP N-terminal segment were replaced by glycine or alanine. With the help of direct carbohydrate analysis and MS, it was found that the acetylated N-terminal peptides of both wildtype strains are glycosylated by a single monosaccharide residue (galactose or fucose) at NAcSer in the first position of the CP sequence, whereas the acetylated N-terminal segment of the ST mutant CP is unglycosylated. Fourier transform infrared spectra in the 1000-4000 cm )1 region were measured for films of the intact and in situ trypsindegraded PVX preparations at low and high humidity. These spectra revealed the presence of a broad-band in the region of valent vibrations of OH bonds (3100-3700 cm )1 ), which can be represented by superposition of three bands corresponding to tightly bound, weakly bound, and free OH groups. On calculating difference (ÔwetÕ minus ÔdryÕ) spectra, it was found that the intact wild-type PVX virions are characterized by high water-absorbing capacity and the ability to order a large number of water molecules on the virus particle. This effect was much weaker for the ST mutant and completely absent in the trypsin-treated PVX. It is proposed that the surface-located and glycosylated N-terminal CP segments of intact PVX virions induce the formation of a columnar-type shell from bound water molecules around the virions, which probably play a major role in maintaining the virion surface structure.

Self carbohydrate-mediated dimerization of glycoprotein angiotensin-converting enzyme (ACE) was demonstrated. The dimerization was studied in the reverse micelle experimental system as a model of biomembrane situation. Asialo-ACE or agalacto-ACE was able to form a dimer, whereas deglycosylated ACE and sequentially desialylated and degalactosylated ACE failed to dimerize. ACE-ACE interaction was competitively inhibited by Neu5Ac- or Gal-terminated saccharides. The results have allowed us to propose the existence of carbohydrate-recognizing domain (CRD) on ACE molecule. The structural requirements of this CRD were estimated based on the ability of saccharides to inhibit ACE dimerization. The most effective monosaccharides with equal inhibition potencies were shown to be galactose (as GalbetaOMe) and N-acetylneuraminic acid (as Neu5AcalphaOMe). Among oligosaccharides, the most effective ones were found to be 3'SiaLac and, especially, the whole pool of ACE oligosaccharide chains and biantennae complex oligosaccharide chains of other glycoproteins. Bovine and human ACEs were shown to be similar in terms of recognition of carbohydrates.

Self carbohydrate‐mediated dimerization of glycoprotein angiotensin‐converting enzyme (ACE) was demonstrated. The dimerization was studied in the reverse micelle experimental system as a model of biomembrane situation. Asialo‐ACE or agalacto‐ACE was able to form a dimer, whereas deglycosylated ACE and sequentially desialylated and degalactosylated ACE failed to dimerize. ACE–ACE interaction was competitively inhibited by Neu5Ac‐ or Gal‐terminated saccharides. The results have allowed us to propose the existence of carbohydrate‐recognizing domain (CRD) on ACE molecule. The structural requirements of this CRD were estimated based on the ability of saccharides to inhibit ACE dimerization. The most effective monosaccharides with equal inhibition potencies were shown to be galactose (as GalβOMe) and N‐acetylneuraminic acid (as Neu5AcαOMe). Among oligosaccharides, the most effective ones were found to be 3′SiaLac and, especially, the whole pool of ACE oligosaccharide chains and biantennae complex oligosaccharide chains of other glycoproteins. Bovine and human ACEs were shown to be similar in terms of recognition of carbohydrates. Copyright © 2000 John Wiley & Sons, Ltd.

The mechanisms of the antiproliferative effect of acacid glycoprotein (AGP) isolated from the blood of healthy donors (nAGP) and from the ascitic fluid of patients with stomach cancer (aAGP) are studied. Three fractions of AGP are divided into 3 groups according to their ability to bind to concanavalin A (ConA): AGP not binding to ConA (AGP-1) and AGP weakly (AGP-2) and strongly (AGP-3) binding to CortA. It is shown that native preparation of aAGP has a more potent inhibitory effect on lymphocyte proliferation than native preparation of nAGP. The most potent inhibitory effect is exerted by AGP-3. Native preparation of aAGP does not affect the secretion of intefleukin-2 (IL-2) by lymphocytes, whereas AGP-1 inhibits this process. The weakly bound fraction has a stimulatory effect both on the proliferative response and on IL-2 secretion.Key Words: orosomycoid; lymphocyte proliferation; interleukin-2 production al-Acid glycoprotein (orosomucoid) is an acute phase protein that may play an important role in the adaptation of the immune system to stress. Experimental data suggest that AGP is a naturally occurring immunomodulating agent which is present in blood serum in both health and pathology (neoplasms, rheumatoid arthritis, burn disease), and its blood level in the latter case may be 2-to 5-fold higher than normal [8,9,12]. There is evidence indicating that in some pathological processes an increase in the blood content of AGP is paralleled by structural changes in the hydrocarbon chains of this glycoprotein, which may affect its biological activity [8]. It has also been demonstrated that AGP with different degrees of glycosylation vary in the ability to inhibit the proliferation of cultured lymphocytes [6,11].Research Center for Medical Genetics, Russian Academy of Medical Sciences; Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow; Immunopreparat Conglomerate, UfaIn this study we attempted to investigate some mechanisms of the antiproliferative activity of various AGP forms that differ in degree of glycosylation. For this purpose we assessed in a wide dose range the ability of AGP preparations to inhibit the proliferation of lymphocytes and examined the effect of these preparations on the secretion of interleukin-2 (IL-2) by these ceUs. MATERIALS AND METHODSAGP was purified from the blood of healthy donors and from the ascitic fluid of patients with stomach cancer, as described elsewhere [1,5]. Fractionation by the glycosylation level was performed on a ConA-Sepharose column as described previously [4]. Three AGP fractions were obtained: not binding (AGP-1), weakly binding (AGP-2), and strongly binding (AGP-3) to CortA. The immunomodulating effects of these preparations were stud-0007-4888/94/0007-0755512.50 @1995 Plenum Publishing Corporation