Cupricyclins, Novel Redox-Active Metallopeptides Based on Conotoxins Scaffold

Highly stable natural scaffolds which tolerate multiple amino acid substitutions represent the ideal starting point for the application of rational redesign strategies to develop new catalysts of potential biomedical and biotechnological interest. The knottins family of disulphide-constrained peptides display the desired characteristics, being highly stable and characterized by hypervariability of the inter-cysteine loops. The potential of knottins as scaffolds for the design of novel copper-based biocatalysts has been tested by engineering a metal binding site on two different variants of an ω-conotoxin, a neurotoxic peptide belonging to the knottins family. The binding site has been designed by computational modelling and the redesigned peptides have been synthesized and characterized by optical, fluorescence, electron spin resonance and nuclear magnetic resonance spectroscopy. The novel peptides, named Cupricyclin-1 and -2, bind one Cu2+ ion per molecule with nanomolar affinity. Cupricyclins display redox activity and catalyze the dismutation of superoxide anions with an activity comparable to that of non-peptidic superoxide dismutase mimics. We thus propose knottins as a novel scaffold for the design of catalytically-active mini metalloproteins

Moisture variability over the Indo-Pacific region and its influence on the Indian summer monsoon rainfall

The Indo-Pacific Ocean (i.e. region between 30E and 150E) has been experiencing a spread warming since the 1950s. At the same time the large-scale summer monsoon rainfall over India and the moisture over the East Africa/Arabian Sea are both decreasing. In this study we intend to investigate how the decrease of moisture over the East Africa/Arabian Sea is related with the Indo-Pacific Ocean warming and how this could affect the variability of the Indian summer monsoon rainfall. We performed the analysis for the period 1951-2012 based on observed precipitation, sea surface temperature and atmospheric reanalysis products and we verified the robustness of the result by comparing different datasets. The decreasing trend of moisture over the East Africa/Arabian Sea coincides with an increasing trend of moisture over the western Pacific region. This is accompanied by the strengthening (weakening) of the upward motion over the western Pacific (East Africa/Arabian Sea) that, consequently, contributes in strengthening the western Pacific-Indian Ocean Walker circulation. Associated with it, the low-level westerlies are weakening over the peninsular India, thus contributing to the reduction of moisture transport towards India. Therefore, rainfall has decreased over the Western Ghats and central-east India. Differently from previous decades, since 2003 moisture over the East Africa/Arabian Sea started to increase and this is accompanied by the strengthening of convection due to increased warming of sea surface temperature over the western Arabian Sea. Despite this moisture increase over the Arabian sea, we found that moisture transport is still weakening over the Indian landmass in the very recent decade and still contributing to the decreased precipitation over the northeast India and southern part of the Western Ghats

Synthetic cascades are enabled by combining biocatalysts with artificial metalloenzymes

Enzymic catalysis and homogeneous catalysis offer complementary means to address synthetic challenges, both in chem. and in biol.  Despite its attractiveness, the implementation of concurrent cascade reactions that combine an organometallic catalyst with an enzyme has proven challenging because of the mutual inactivation of both catalysts.  To address this, we show that incorporation of a d6-piano stool complex within a host protein affords an artificial transfer hydrogenase (ATHase) that is fully compatible with and complementary to natural enzymes, thus enabling efficient concurrent tandem catalysis.  To illustrate the generality of the approach, the ATHase was combined with various NADH-, FAD- and haem-dependent enzymes, resulting in orthogonal redox cascades.  Up to three enzymes were integrated in the cascade and combined with the ATHase with a view to achieving (i) a double stereoselective amine deracemization, (ii) a horseradish peroxidase (HRP)-coupled readout of the transfer hydrogenase activity towards its genetic optimization, (iii) the formation of L-pipecolic acid from L-lysine, and (iv) regeneration of NADH to promote a monooxygenase-catalyzed oxyfunctionalization reactio

Protein Design: Toward Functional Metalloenzymes

The scope of this Review is to discuss the construction of metal sites in designed protein scaffolds. We categorize the effort of designing proteins into redesign, which is to rationally engineer desired functionality into an existing protein scaffold,(1-9) and de novo design, which is to build a peptidic or protein system that is not directly related to any sequence found in nature yet folds into a predicted structure and/or carries out desired reactions.(10-12) We will analyze and interpret the significance of designed protein systems from a coordination chemistry and biochemistry perspective, with an emphasis on those containing constructed metal sites as mimics for metalloenzymes