Biomedical subjects

M Vihinen

Publications and source records attributed to M Vihinen.

95 records · Page 6Linked to original sources

PubMed1990

Characterization of a thermostable Bacillus stearothermophilus alpha-amylase.

Liquefying-type Bacillus stearothermophilus alpha-amylase was characterized. The coding gene was cloned in Bacillus subtilis and the enzyme was produced in three different host organisms: B. stearothermophilus, B. subtilis, and Escherichia coli. Properties of the purified enzyme were similar irrespective of the host. Temperature optimum was at 70-80 degrees C and pH optimum at 5.0-6.0. The enzyme was stable for 1 h in the pH range 6.0-7.5 at 80 degrees C. The enzyme was stabilized by Ca2+, Na+, and bovine serum albumin. About 50% of the activity remained after heating at 70 degrees C for 5 days or 45 min at 90 degrees C. Metal ions Cd2+, Cu2+, Hg2+, Pb2+, and Zn2+ were inhibitory, whereas EDTA, ethylene glycol bis(beta-aminoethyl ether) N,N,N',N'-tetraacetic acid, and Tendamistat were without effect. The enzyme was fully active after treatment in acetone or ethanol at 55 or 70 degrees C, respectively, for 30 min. Sodium dodecyl sulfate (1%) did not affect stability, whereas 6 M urea denatured totally at 70 degrees C. The Km value for soluble starch was 14 mg/ml. Mr is 59,000 and pI 8.8. The only difference between the enzymes produced in different hosts was in signal peptide processing.

Amino Acid Sequence↗

PubMed1989

Microbial amylolytic enzymes.

Starch-degrading, amylolytic enzymes are widely distributed among microbes. Several activities are required to hydrolyze starch to its glucose units. These enzymes include alpha-amylase, beta-amylase, glucoamylase, alpha-glucosidase, pullulan-degrading enzymes, exoacting enzymes yielding alpha-type endproducts, and cyclodextrin glycosyltransferase. Properties of these enzymes vary and are somewhat linked to the environmental circumstances of the producing organisms. Features of the enzymes, their action patterns, physicochemical properties, occurrence, genetics, and results obtained from cloning of the genes are described. Among all the amylolytic enzymes, the genetics of alpha-amylase in Bacillus subtilis are best known. Alpha-Amylase production in B. subtilis is regulated by several genetic elements, many of which have synergistic effects. Genes encoding enzymes from all the amylolytic enzyme groups dealt with here have been cloned, and the sequences have been found to contain some highly conserved regions thought to be essential for their action and/or structure. Glucoamylase appears usually in several forms, which seem to be the results of a variety of mechanisms, including heterogeneous glycosylation, limited proteolysis, multiple modes of mRNA splicing, and the presence of several structural genes.

Bacteria↗

PubMed1988

An algorithm for simultaneous comparison of several sequences.

An algorithm was developed to compare simultaneously several DNA, RNA or protein sequences. With the algorithm, conserved regions of one sequence are located by doing pairwise comparisons with other sequences, which is advantageous in planning site-directed mutagenesis studies. The observation matrices filled with scores of comparisons are superimposed and added together and those points having values greater than or equal to stringency are accepted. The predicted secondary structural features can also be compared.

Algorithms↗

PubMed1987

Relationship of protein flexibility to thermostability.

Thermostability of proteins arises from the simultaneous effect of several forces, which in fact lead to decreased flexibility of the polypeptide chain. This is verified by flexibility indices, which are derived from normalized B-values of individual amino acids in several refined three-dimensional structures. Flexibility indices show that overall flexibility is reduced when thermostability is increased. Protein molecules require both flexibility and rigidity to function, but the higher the temperature optimum and stability the more rigid is the structure needed to compensate for increased thermal fluctuations. Flexibilities of proteins performing the same catalytic activity seem to be about the same at their temperature optima, but the more rigid thermostable proteins reach the flexibility of thermolabile proteins at higher temperatures. In several proteins such as allosteric enzymes, some local sites of flexibility are highly conserved. The relevance of reduced flexibility to overall stability of proteins is also discussed. Flexibility indices and profiles can be used in the design of more stable proteins by site-directed mutagenesis.

Mutation↗

PubMedDate not supplied

Structural analysis of an anti-estradiol antibody.

An anti-estradiol antibody with improved specificity is searched for by combining steroid analog binding studies, mutant antibodies obtained from a phage-display library and structural modeling. Three-dimensional models for the anti-estradiol antibody 57-2 were constructed by comparative model building. Estradiol and analogs were docked into the combining site and molecular dynamics simulation was used to further refine this area of the protein. Cross-reactivities measured against 36 steroid analogs were used to help in the docking process and to evaluate the models. The roles of a number of residues were assessed by characterization of cross-reactivity mutants obtained from a phage display library. The cross-reactivity data and the results observed for mutants are explained by the structural model, in which the estradiol D-ring inserts deeply into the binding site and interacts with the antibody through at least one specific hydrogen bond. The binding data strongly suggest that this hydrogen bond connects the estradiol 17-hydroxyl group with the side chain of Gln H35. As expected for the binding of a small aromatic molecule, the antibody binding site contains many aromatic residues, e.g. Trp H50, H95 and L96 and Tyr L32, L49 and Phe L91.

Amino Acid Sequence↗