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S D'Amico

Publications and source records attributed to S D'Amico.

At least 19 recordsLinked to original sources
PubMed2006

Cold-adapted enzymes from marine Antarctic microorganisms.

The Antarctic marine environment is characterized by challenging conditions for the survival of native microorganisms. Indeed, next to the temperature effect represented by the Arrhenius law, the viscosity of the medium, which is also significantly enhanced by low temperatures, contributes to slow down reaction rates. This review analyses the different challenges and focuses on a key element of life at low temperatures: cold-adapted enzymes. The molecular characteristics of these enzymes are discussed as well as the adaptation strategies which can be inferred from the comparison of their properties and three-dimensional structures with those of their mesophilic counterparts. As these enzymes display a high specific activity at low and moderate temperatures associated with a relatively high thermosensitivity, the interest in these properties is discussed with regard to their current and possible applications in biotechnology.

Adaptation, Physiological↗
PubMed2006

Kinetics and energetics of ligand binding determined by microcalorimetry: insights into active site mobility in a psychrophilic alpha-amylase.

A new microcalorimetric method for recording the kinetic parameters k(cat), K(m) and K(i) of alpha-amylases using polysaccharides and oligosaccharides as substrates is described. This method is based on the heat released by glycosidic bond hydrolysis. The method has been developed to study the active site properties of the cold-active alpha-amylase produced by an Antarctic psychrophilic bacterium in comparison with its closest structural homolog from pig pancreas. It is shown that the psychrophilic alpha-amylase is more active on large macromolecular substrates and that the higher rate constants k(cat) are gained at the expense of a lower affinity for the substrate. The active site is able to accommodate larger inhibitory complexes, resulting in a mixed-type inhibition of starch hydrolysis by maltose. A method for recording the binding enthalpies by isothermal titration calorimetry in a low-affinity system has been developed, allowing analysis of the energetics of weak ligand binding using the allosteric activator chloride. It is shown that the low affinity of the psychrophilic alpha-amylase for chloride is entropically driven. The high enthalpic and entropic contributions of activator binding suggest large structural fluctuations between the free and the bound states of the cold-active enzyme. The kinetic and thermodynamic data for the psychrophilic alpha-amylase indicate that the strictly conserved side-chains involved in substrate binding and catalysis possess an improved mobility, responsible for activity in the cold, and resulting from the disappearance of stabilizing interactions far from the active site.

Animals↗
PubMed2005

Predictors of glycaemic control in indigent patients presenting with diabetic ketoacidosis.

AIM: To derive predictors of good glycaemic control in patients presenting with diabetic ketoacidosis (DKA) followed prospectively in a specialized clinic. METHODS: One hundred and sixty-one adult patients were admitted during a 31-month period and followed for at least 12 months. After 1 year, the patients were classified into three groups: good control (GC) (HbA1c < or = 7%), intermediate control (IC) (HbA1c 7-9%) and poor control (PC) (HbA1c > 9%). Characteristics of patients in the three groups were compared both at baseline and during follow-up. RESULTS: At 12 months, 36% of the patients were classified as GC, 27% as IC and 37% as PC. GC patients had higher fasting serum C-peptide levels 0.7 +/- 0.54 compared to 0.38 +/- 0.29 and 0.16 +/- 0.21 nmol/l, respectively, for the IC and PC patients (p < 0.0001). A higher proportion GC patient had a C-peptide level greater than 0.33 nmol/l than that for IC and PC patients (86, 61 and 19%, respectively; p < 0.0001). Exogenous insulin was safely discontinued in 50, 30 and 3% of patients, respectively, in the GC, IC and PC groups (p < 0.0001). Compliance with life-style interventions was higher in the GC than that in IC and PC patients (87, 41 and 5%, respectively; p < 0.0001). In the logistic regression analysis, predictors of good glycaemic control were having baseline fasting serum C-peptide value > or =0.33 mmol/l, OR: 3.01 (95% CI 1.07-8.55, p = 0.03) and compliance with life-style interventions OR 12.66 (95% CI 3.73-51.57, p = 0.0001). CONCLUSION: Among adult patients with DKA, significant predictors of good glycaemic control are preserved beta-cell function and compliance with life-style modifications.

Adult↗
PubMed2004

Separate neural systems for processing action- or non-action-related sounds.

The finding of a multisensory representation of actions in a premotor area of the monkey brain suggests that similar multimodal action-matching mechanisms may also be present in humans. Based on the existence of an audiovisual mirror system, we investigated whether sounds referring to actions that can be performed by the perceiver underlie different processing in the human brain. We recorded multichannel ERPs in a visuoauditory version of the repetition suppression paradigm to study the time course and the locus of the semantic processing of action-related sounds. Results show that the left posterior superior temporal and premotor areas are selectively modulated by action-related sounds; in contrast, the temporal pole is bilaterally modulated by non-action-related sounds. The present data, which support the hypothesis of distinctive action sound processing, may contribute to recent theories about the evolution of human language from a mirror system precursor.

Acoustic Stimulation↗
PubMed2004

Some like it cold: biocatalysis at low temperatures.

In the last few years, increased attention has been focused on a class of organisms called psychrophiles. These organisms, hosts of permanently cold habitats, often display metabolic fluxes more or less comparable to those exhibited by mesophilic organisms at moderate temperatures. Psychrophiles have evolved by producing, among other peculiarities, "cold-adapted" enzymes which have the properties to cope with the reduction of chemical reaction rates induced by low temperatures. Thermal compensation in these enzymes is reached, in most cases, through a high catalytic efficiency associated, however, with a low thermal stability. Thanks to recent advances provided by X-ray crystallography, structure modelling, protein engineering and biophysical studies, the adaptation strategies are beginning to be understood. The emerging picture suggests that psychrophilic enzymes are characterized by an improved flexibility of the structural components involved in the catalytic cycle, whereas other protein regions, if not implicated in catalysis, may be even more rigid than their mesophilic counterparts. Due to their attractive properties, i.e., a high specific activity and a low thermal stability, these enzymes constitute a tremendous potential for fundamental research and biotechnological applications.

Adaptation, Physiological↗
PubMed2004

Ambipolar transistors based on azurin proteins.

A new type of transistor is presented. It is realised by using a metalloprotein; namely, azurin. Thanks to their natural functional characteristics, which involve inter- and intramolecular electron transfer, metalloproteins are good candidates for biomolecular nanoelectronics. The implementation of a prototype of protein transistor operating in air and in the solid state based on self-organised films of azurins is reported. Experimental current-voltage characteristics are shown. The new device presents an ambipolar behaviour as the gate bias voltage is changed. Exploiting this peculiar characteristic, a fully integrated logic gate which can be a good starting point for a new class of nanoelectronics devices has been realised.

Journal Article↗
PubMed2004

A perspective on cold enzymes: current knowledge and frequently asked questions.

Studies on psychrophilic enzymes to determine the structural features important for cold-activity have attracted increased attention in the last few years. This enhanced interest is due to the attractive properties of such proteins, i.e. a high specific activity and a low thermal stability, and thus, these enzymes constitute a tremendous potential for fundamental research and biotechnological applications. This review examines the impact of low temperatures on life, the diversity of adaptation to counteract these effects and gives an overview of the features proposed to account for low thermal stability and cold-activity, following the chronological order of the catalytic cycle phases. Moreover, we present an overview of recent techniques used in the analysis of the flexibility of a protein structure which is an important concept in cold-adaptation; an overview of biotechnological potential of psychrophilic enzymes and finally, a few frequently asked questions about cold-adaptation and their possible answers.

Adaptation, Physiological↗
PubMed2001

Structural determinants of cold adaptation and stability in a large protein.

The heat-labile alpha-amylase from an antarctic bacterium is the largest known protein that unfolds reversibly according to a two-state transition as shown by differential scanning calorimetry. Mutants of this enzyme were produced, carrying additional weak interactions found in thermostable alpha-amylases. It is shown that single amino acid side chain substitutions can significantly modify the melting point T(m), the calorimetric enthalpy Delta H(cal), the cooperativity and reversibility of unfolding, the thermal inactivation rate constant, and the kinetic parameters k(cat) and K(m). The correlation between thermal inactivation and unfolding reversibility displayed by the mutants also shows that stabilizing interactions increase the frequency of side reactions during refolding, leading to intramolecular mismatches or aggregations typical of large proteins. Although all mutations were located far from the active site, their overall trend is to decrease both k(cat) and K(m) by rigidifying the molecule and to protect mutants against thermal inactivation. The effects of these mutations indicate that the cold-adapted alpha-amylase has lost a large number of weak interactions during evolution to reach the required conformational plasticity for catalysis at low temperatures, thereby producing an enzyme close to the lowest stability allowing maintenance of the native conformation.

Bacterial Proteins↗
PubMed2001

Did psychrophilic enzymes really win the challenge?

Organisms living in permanently cold environments, which actually represent the greatest proportion of our planet, display at low temperatures metabolic fluxes comparable to those exhibited by mesophilic organisms at moderate temperatures. They produce cold-evolved enzymes partially able to cope with the reduction in chemical reaction rates and the increased viscosity of the medium induced by low temperatures. In most cases, the adaptation is achieved through a reduction in the activation energy, leading to a high catalytic efficiency, which possibly originates from an increased flexibility of either a selected area of or the overall protein structure. This enhanced plasticity seems in return to be responsible for the weak thermal stability of cold enzymes. These particular properties render cold enzymes particularly useful in investigating the possible relationships existing between stability, flexibility, and specific activity and make them potentially unrivaled for numerous biotechnological tasks. In most cases, however, the adaptation appears to be far from being fully achieved.

Adaptation, Physiological↗
PubMed2001

Word reading and picture naming in Italian.

Results from two separate norming studies of lexical access in Italian were merged, permitting a comparison of word-reading and picture-naming latencies and the factors that predict each one for an overlapping subsample of 128 common nouns. Factor analysis of shared lexical predictors yielded four latent variables: a frequency factor, a semantic factor, a length factor, and a final factor dominated by frication on the initial phoneme. Age of acquisition (AoA) loaded highly on the first two factors, suggesting that it can be split into separate sources of variance. Regression analyses using factor scores as predictors showed that word reading and picture naming are both influenced by the frequency/AoA factor. The semantics/AoA factor influenced only picture naming, whereas the length and frication factors influenced only word reading. Generalizability of these results to other languages is discussed, including potential effects of cross-language differences in orthographic transparency.

Adult↗
PubMed2000

Structural similarities and evolutionary relationships in chloride-dependent alpha-amylases.

The alpha-amylase sequences contained in databanks were screened for the presence of amino acid residues Arg195, Asn298 and Arg/Lys337 forming the chloride-binding site of several specialized alpha-amylases allosterically activated by this anion. This search provides 38 alpha-amylases potentially binding a chloride ion. All belong to animals, including mammals, birds, insects, acari, nematodes, molluscs, crustaceans and are also found in three extremophilic Gram-negative bacteria. An evolutionary distance tree based on complete amino acid sequences was constructed, revealing four distinct clusters of species. On the basis of multiple sequence alignment and homology modeling, invariable structural elements were defined, corresponding to the active site, the substrate binding site, the accessory binding sites, the Ca(2+) and Cl(-) binding sites, a protease-like catalytic triad and disulfide bonds. The sequence variations within functional elements allowed engineering strategies to be proposed, aimed at identifying and modifying the specificity, activity and stability of chloride-dependent alpha-amylases.

Amino Acid Sequence↗
PubMed2000

Cold-adapted enzymes: from fundamentals to biotechnology.

Psychrophilic enzymes produced by cold-adapted microorganisms display a high catalytic efficiency and are most often, if not always, associated with high thermosensitivity. Using X-ray crystallography, these properties are beginning to become understood, and the rules governing their adaptation to cold appear to be relatively diverse. The application of these enzymes offers considerable potential to the biotechnology industry, for example, in the detergent and food industries, for the production of fine chemicals and in bioremediation processes.

Adaptation, Physiological↗
PubMed1999

Effect of grammatical gender and semantic context on lexical access in Italian.

The interacting effects of sentence context and grammatical gender on lexical access were investigated in Italian using a timed picture-naming paradigm. Results showed large interacting effects of both sentence context and the gender of the article, with facilitation relative to two different control conditions. Repeat testing yielded an overall decrease in RT, but did not change the pattern of results. Results are interpreted in support of interactive activation models in which different sources of information are combined "on-line" to predict, anticipate or preactivate lexical targets.

Adult↗
PubMed1998

Characterization of the C-terminal propeptide involved in bacterial wall spanning of alpha-amylase from the psychrophile Alteromonas haloplanctis.

The antarctic psychrophile Alteromonas haloplanctis secretes a Ca2+- and Cl--dependent alpha-amylase. The nucleotide sequence of the amy gene and the amino acid sequences of the gene products indicate that the alpha-amylase precursor is a preproenzyme composed by the signal peptide (24 residues), the mature alpha-amylase (453 residues, 49 kDa), and a long C-terminal propeptide or secretion helper (192 residues, 21 kDa). In cultures of the wild-type strain, the 70-kDa precursor is secreted at the mid-exponential phase and is cleaved by a nonspecific protease into the mature enzyme and the propeptide. The purified C-terminal propeptide displays several features common to beta-pleated transmembrane proteins. It has no intramolecular chaperone function because active alpha-amylase is expressed by Escherichia coli in the absence of the propeptide coding region. In E. coli, the 70-kDa precursor is directed toward the supernatant. When the alpha-amylase coding region is excised from the gene, the secretion helper can still promote its own membrane spanning. It can also accept a foreign passenger, as shown by the extracellular routing of a beta-lactamase-propeptide fusion protein.

Amino Acid Sequence↗
PubMed1995

Assessment of the value of treatment with granulocyte colony-stimulating factor in children with acute lymphoblastic leukemia: a randomized clinical trial.

The present trial was designed to test the effects of G-CSF on the duration of the second phase of induction chemotherapy in children with newly diagnosed acute lymphoblastic leukemia (ALL). A total of 32 patients were assigned randomly to a group that received (14 patients; group A) or a group that did not receive (18 patients; group B) G-CSF (10 g/kg/day subcutaneously and daily) throughout of the second phase of induction therapy. One of 14 (7.1%) patients in group A and 2 of 18 (11.1%) patients in group B completed the course of chemotherapy within the planned time. The median length of this phase was 37 days (range, 29 to 65; mean, 40; SD, 8.6) for patients in group A and 36 days (range, from 29 to 55; mean, 38; SD, 7.4) for those in group B, and the difference was not statistically significant. The number of days during which patients had granulocyte counts of less than 2 x 10(9)/l, the number of febrile episodes of unknown origin, the number of bacterial and fungal infections and the number of days of hospitalization did not differ in a statistically significant manner between the two groups. Our data suggest that G-CSF supportive therapy may be unnecessary in children with neutropenia of short duration, for whom the risk of infection is low.

Adolescent↗
PubMed1995

Gender and lexical access in Italian.

Two new procedures were employed to investigate the effects of semantic and grammatical gender on lexical access in Italian and to investigate the interaction of gender with other factors that are known to influence lexical access in other languages. The gender-monitoring task requires a conscious decision about the gender of each noun, whereas the word repetition task does not require explicit attention to gender. In both tasks, single words are presented out of context, under speeded conditions. Both procedures proved to be sensitive indices of word recognition, with reaction times that are closely tied to the point at which words can be uniquely identified (although some processing before and after the uniqueness point was seen). In both tasks, reaction times were strongly affected by phonological factors (e.g., length, number of syllables, and presence of frication on the initial consonant). Phonological transparency of gender marking had a reliable effect on gender monitoring but had no effect on word repetition, suggesting that explicit attention to gender may be a factor affecting utilization of this phonological cue. Semantic factors (including semantic gender) had no effect on performance. Frequency and age of acquisition had very small effects when other factors were controlled. Implications for current models of lexical access are discussed, with special reference to the role of gender.

Humans↗