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Despite the importance of Mg2+ for numerous cellular activities, the mechanisms underlying its import and homeostasis are poorly understood. The CorA family is ubiquitous and is primarily responsible for Mg2+ transport. However, the key questions-such as, the ion selectivity, the transport pathway, and the gating mechanism-have remained unanswered for this protein family. We present a 3.2 Å resolution structure of the archaeal CorA from Methanocaldococcus jannaschii, which is a unique complete structure of a CorA protein and reveals the organization of the selectivity filter, which is composed of the signature motif of this family. The structure reveals that polar residues facing the channel coordinate a partially hydrated Mg2+ during the transport. Based on these findings, we propose a unique gating mechanism involving a helical turn upon the binding of Mg2+ to the regulatory intracellular binding sites, and thus converting a polar ion passage into a narrow hydrophobic pore. Because the amino acids involved in the uptake, transport, and gating are all conserved within the entire CorA family, we believe this mechanism is general for the whole family including the eukaryotic homologs. [ABSTRACT FROM AUTHOR]

Obtaining mono-disperse and stable protein is a requirement for successful structural and biochemical investigation of proteins. For membrane proteins, such preparation is one of the major hurdles, which consequently has contributed to the slow progress in studying them. During the past few years, many screening methods have been developed to make studies of membrane proteins more efficient. Despite these advances, many membrane proteins remain challenging to even isolate in a stable and homogeneous form. The bacterial zinc transporter ZntB is such a protein, for which no isolation procedure has been reported. Here, we present a systematic approach to obtain homogeneous and mono-disperse zinc transporter ZntB in quantities sufficient for structural and biochemical studies. Important aspects of this study that can be applied to other membrane proteins are also discussed., (Copyright 2010 Elsevier Inc. All rights reserved.)

The Kaposi's sarcoma-associated herpesvirus protein SOX (shut off and exonuclease) and its Epstein-Barr virus homolog, BGLF5, are active during the early lytic phase and belong to the alkaline nuclease family. Both proteins have been shown to be bifunctional, being responsible for DNA maturation as well as host shutoff at the mRNA level. We present the crystal structure of SOX determined at 1.85 A resolution. By modeling DNA binding, we have identified catalytic residues that explain the preferred 5'-exonuclease activity of the alkaline nucleases. The presence of a crevice suitable for binding duplex DNA supports a role for herpes alkaline nucleases in recombination events preceding packaging of viral DNA. Direct interaction with dsDNA is supported by oligonucleotide binding data. Mutations specifically affecting host shutoff map to a surface region of the N-terminal domain, implying an essential role in protein-protein interactions, and link the RNase activity of the enzyme to mRNA degradation pathways.