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Agkisacucetin is a snake C-type lectin isolated from the venom of Agkistrodon acutus (A. acutus). It binds specifically to the platelet glycoprotein (GP) Ib and prevents the von Willebrand factor (VWF) accessing it. We determined the crystal structure of agkisacucetin to 1.9A resolution. The structure of agkisacucetin has an (αβ) fold similar to another GPIb-binding protein, flavocetin-A, but lacks the C-terminal cysteine in the β-subunit, does not form (βα)4 tetramers, and does not cluster GPIbs, like flavocetin-A. Proteins 2012;. © 2012 Wiley Periodicals, Inc.

Transcription in archaea employs a eukaryotic-type transcription apparatus but uses bacterial-type transcription factors. NusG is one of the few archaeal transcription factors whose orthologs are essential in both bacteria and eukaryotes. Archaeal NusG is composed of only an NusG N-terminal (NGN) domain and a KOW domain, which is similar to bacterial NusG but not to the eukaryotic ortholog, Spt5. However, archaeal NusG was confirmed recently to form a complex with rpoE″ that was similar to the Spt5-Spt4 complex. Thus, archaeal NusG presents hybrid features of Spt5 and bacterial NusG. Here we report the crystal structure of NGN from the archaea Methanocaldococcus jannaschii (MjNGN). MjNGN folds to an α-β-α sandwich without the appendant domain of bacterial NGNs, and forms a unique homodimer in crystal and solution. MjNGN alone was found to be sufficient for rpoE″ binding and an MjNGN-rpoE″ model has been constructed by rigid docking. Proteins 2009. © 2009 Wiley-Liss, Inc.

Snake secreted phospholipasesA2 (sPLA2s) are widely used as pharmacological tools to investigate their role in diverse pathophysiological processes. Some members of snake venom sPLA2s have been found to block voltage-activated K(+) channels (K(v) channels). However, most studies involved in their effects on ion channels were indirectly performed on motor nerve terminals while few studies were directly done on native neurons. Here, a novel snake sPLA2 peptide neurotoxin, Natratoxin, composed of 119 amino acid residues and purified from Naja atra venom was reported. It was characterized using whole-cell patch-clamp in acutely dissociated rat dorsal root ganglion (DRG) neurons. It was found to effectively inhibit A-type K(+) currents and cause alterations of channel gating characters, such as the shifts of steady-state activation and inactivation curves to hyperpolarization direction and changes of V(1/2) and slope factor. Therefore, Natratoxin was suggested to be a gating modifier of K(v) channel. In addition, this inhibitory effect was found to be independent of its enzymatic activity. These results suggested that the toxin enacted its inhibitory effect by binding to K(v) channel. To further elucidate the structural basis for this electrophysiological phenomenon, we determined the crystal structure of Natratoxin at 2.2 A resolution by molecular replacement method and refined to an R-factor of 0.190. The observed overall fold has a different structural organization from other K(+) channel inhibitors in animal toxins. Compared with other K(v) channel inhibitors, a similar putative functional surface in its C-terminal was revealed to contribute to protein-protein interaction in such a blocking effect. Our results demonstrated that the spatial distribution of key amino acid residues matters most in the recognition of this toxin towards its channel target rather than its type of fold.