Is the binding of magnesium (II) to calmodulin significant? An investigation by magnesium-25 nuclear magnetic resonance

Previous reports on the interaction between calmodulin (CaM) and Mg2+ range from no binding to a binding constant of 10(4) M-1 [for a summary, see Cox, J. A., Comte, M., Malnoe, A., Berger, D., & Stein, E. A. (1984) Met. Ions Biol. Syst. 17, 215-273]. In order to resolve the controversy, we used 25Mg NMR to study the binding of Mg2+ to apo-CaM, CaM.Ca2(2)+ (in which sites III and IV are occupied by Ca2+), CaM.La2(3)+ (in which sites I and II are occupied by La3+), and the two tryptic fragments of calmodulin, TR1C (containing sites I and II of CaM) and TR2C (containing sites III and IV of CaM). In each system, a "titration set" and a "temperature set" were obtained, and the spectral data were analyzed by total band-shape analysis to calculate the association constant (Ka) and off-rate (koff). As in the case of Ca2+ binding, sites I and II and sites III and IV were treated as two sets of equivalent sites, and a Ca2+/Mg2+ competition experiment suggested that Mg2+ competes with Ca2+ for the same sites. For both CaM.Ca2(2)+ and TR1C, moderately large Ka (2000 and 3500 M-1, respectively) and moderate off-rates (koff = 2300 and 3000 s-1, respectively, at 25 degrees C) were observed. For both CaM.La2(3)+ and TR2C, binding of Mg2+ was weaker by a factor of ca. 10 (Ka = 300 and 200 M-1, respectively) while the off-rates were also moderate (koff = 3500 and 2200 s-1, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)     

Isolation and characterization of an induced chondroitinase ABC from Flavobacterium heparinum

During the investigation of alternative methods for the large scale preparation of chondroitinases AC, B and C from Flavobacterium heparinum, a new chondroitinase activity was observed. This new enzyme, like the other chondroitinases, acts as an eliminase, forming unsaturated sulfated disaccharides from dermatan and chondroitin sulfates. In contrast to the chondroitinases previously described, which are endoglycosidases, this chondroitinase ABC cleaves the glycosidic linkages in an exolytic fashion, beginning at the reducing end of the substrate molecules. The oligosaccharides formed as transient products by the action of either chondroitinases or testicular hyaluronidase upon dermatan and chondroitin sulfates are also rapidly degraded by the chondroitinase ABC, regardless of their size or the presence of delta-4,5 unsaturation in the terminal uronic acid residue. The maximum activity of the chondroitinase ABC occurs at 30 degrees C and at pH 6.0-7.5. Only 15% of the activity was observed at 37 degrees C, indicating that the enzyme is very sensitive to thermal denaturation. It is strongly inhibited by phosphate ions and is also inhibited by the unsaturated disaccharides formed.     

The use of starch and skim milk in the regeneration of Bacillus amylotiquefaciens and Bacillus subtilis protoplasts

The addition of starch or skim milk to bovine serum albumin-containing regeneration medium enhances the regeneration of both Bacillus amyloliquefaciens and B. subtilis protoplasts. With B. amyloliquefaciens starch could replace bovine serum albumin; with B. subtilis either starch or skim milk could be used instead of bovine serum albumin. The maximum regeneration frequency achieved was 10% with B. amyloliquefaciens and 290% with B. subtilis .     

Primary structure of the glycans from mouse serum and milk transferrins.

A 'serotransferrin-like' protein was purified from mouse milk. This serotransferrin cross-reacts immunologically with the serotransferrin isolated from mouse plasma and not with the mouse lactotransferrin (lactoferrin). Sugar analysis of the three transferrins, i.e. serotransferrin, milk 'serotransferrin-like' protein and lactotransferrin, revealed that the major difference between the glycan primary structure of mouse serotransferrin and those of mouse milk 'serotransferrin-like' protein and lactotransferrin concerns essentially the presence of one fucose residue in the last two proteins. For structural determination, the N-glycosidically linked glycans were released from the protein by a reductive cleavage of the oligosaccharide-protein linkage under strong alkaline conditions. The primary structure of the released oligosaccharide alditols was determined by methylation analysis and 400 MHz 1H-n.m.r. spectroscopy. The oligosaccharide alditols released from milk 'serotransferrin-like' protein and lactotransferrin were identical and were identified as disialylated biantennary glycans of the N-acetyl-lactosamine type with a fucose residue alpha-1,6-linked to the N-acetylglucosamine residue conjugated to the peptide chain and having the following primary structure: NeuAc(alpha 2-6)Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-3)[NeuAc(alpha 2-6)Gal(beta 1-4)GlcNAc(beta 1-2)Man(alpha 1-6)]Man(beta 1-4)GlcNAc(beta 1-4)[Fuc(alpha 1-6)]GlcNAc(beta 1-N)Asn. The serotransferrin glycan has the same primary structure but is only partially fucosylated (10-15%).     

Cloning and characterization of LOS1, a Saccharomyces cerevisiae gene that affects tRNA splicing.

Saccharomyces cerevisiae strains carrying los1-1 mutations are defective in tRNA processing; at 37 degrees C, such strains accumulate tRNA precursors which have mature 5' and 3' ends but contain intervening sequences. Strains bearing los1-1 and an intron-containing ochre-suppressing tRNA gene, SUP4(0), also fail to suppress the ochre mutations ade2-1(0) and can1-100(0) at 34 degrees C. To understand the role of the LOS1 product in tRNA splicing, we initiated a molecular study of the LOS1 gene. Two plasmids, YEpLOS1 and YCpLOS1, that complement the los1-1 phenotype were isolated from the YEp24 and YCp50 libraries, respectively. YEpLOS1 and YCpLOS1 had overlapping restriction maps, indicating that the DNA in the overlapping segment could complement los1-1 when present in multiple or single copy. Integration of plasmid DNA at the LOS1 locus confirmed that these clones contained authentic LOS1 sequences. Southern analyses showed that LOS1 is a single copy gene. The locations of the LOS1 gene within YEpLOS1 and YCpLOS1 were determined by deletion and gamma-delta mapping. Two genomic disruptions of the LOS1 gene were constructed, i.e., an insertion of a 1.2-kilobase fragment carrying the yeast URA3 gene, los1::URA3, and a 2.4-kilobase deletion from the LOS1 gene, los1-delta V. Disruption or deletion of most of the LOS1 gene was not lethal; cells carrying the disrupted los1 alleles were viable and had phenotypes similar to those of cells carrying the los1-1 allele. Thus, it appears that the los1 gene product expedites tRNA splicing at elevated temperatures but is not essential for this process.