Structural adaptation to low temperature - analysis of the subunit interface of oligomeric psychrophilic enzymes

Enzymes from psychrophiles show higher catalytic efficiency in the 0-20 degrees C temperature range and often lower thermostability in comparison with meso/thermophilic homologs. Physical and chemical characterization of these enzymes is currently underway in order to understand the molecular basis of cold adaptation. Psychrophilic enzymes are often characterized by higher flexibility, which allows for better interaction with substrates, and by a lower activation energy requirement in comparison with meso/thermophilic counterparts. In their tertiary structure, psychrophilic enzymes present fewer stabilizing interactions, longer and more hydrophilic loops, higher glycine content, and lower proline and arginine content. In this study, a comparative analysis of the structural characteristics of the interfaces between oligomeric psychrophilic enzyme subunits was carried out. Crystallographic structures of oligomeric psychrophilic enzymes, and their meso/thermophilic homologs belonging to five different protein families, were retrieved from the Protein Data Bank. The following structural parameters were calculated: overall and core interface area, characterization of polar/apolar contributions to the interface, hydrophobic contact area, quantity of ion pairs and hydrogen bonds between monomers, internal area and total volume of non-solvent-exposed cavities at the interface, and average packing of interface residues. These properties were compared to those of meso/thermophilic enzymes. The results were analyzed using Student's t-test. The most significant differences between psychrophilic and mesophilic proteins were found in the number of ion pairs and hydrogen bonds, and in the apolarity of their subunit interface. Interestingly, the number of ion pairs at the interface shows an opposite adaptation to those occurring at the monomer core and surface

Investigations on the Karyotype of 40 Chromosome Dwarf Bearded Irises (Third Contribution)

SUMMARYThe study of 40 chromosome dwarf bearded Irises, reported in previous papers, has now been extended to the localities of Monte Marcello, Pozzuolo, San Giuliano Terme, Gabbro, Braccagni, Alberese, La Marsiliana along the banks of the river Albegna and La Marsiliana-Pietricci. A common karyotype, showing slight differences, according to the clones examined and generally referring to the satellites, has been evidenced by means of karyological investigation. In addition to this a brief morphological analysis of the specimens has been carried out at flowering in the Hortum Botanicum Florentinum. The data recorded in Table I show that it is impossible to distinguish different entities in the group of the Irises studied, through karyological analysis. This seems to be confirmed by the few morphological data. More detailed morphological analysis and possibly an investigation on the behaviour of the hybrids, would seem at the moment to be the only way to solve this problem