Calcium binding to a disordered domain of a type III-secreted protein from a coral pathogen promotes secondary structure formation and catalytic activity

Strains of the Gram-negative bacterium Vibrio coralliilyticus cause the bleaching of corals due to decomposition of symbiotic microalgae. The V. coralliilyticus strain ATCC BAA-450 (Vc450) encodes a type III secretion system (T3SS). The gene cluster also encodes a protein (locus tag VIC_001052) with sequence homology to the T3SS-secreted nodulation proteins NopE1 and NopE2 of Bradyrhizobium japonicum (USDA110). VIC_001052 has been shown to undergo auto-cleavage in the presence of Ca2+ similar to the NopE proteins. We have studied the hitherto unknown secondary structure, Ca2+-binding affinity and stoichiometry of the "metal ion-inducible autocleavage" (MIIA) domain of VIC_001052 which does not possess a classical Ca2+-binding motif. CD and fluorescence spectroscopy revealed that the MIIA domain is largely intrinsically disordered. Binding of Ca2+ and other di- and trivalent cations induced secondary structure and hydrophobic packing after partial neutralization of the highly negatively charged MIIA domain. Mass spectrometry and isothermal titration calorimetry showed two Ca2+-binding sites which promote structure formation with a total binding enthalpy of -110 kJ mol(-1) at a low micromolar K-d. Putative binding motifs were identified by sequence similarity to EF-hand domains and their structure analyzed by molecular dynamics simulations. The stoichiometric Ca2+-dependent induction of structure correlated with catalytic activity and may provide a "host-sensing" mechanism that is shared among pathogens that use a T3SS for efficient secretion of disordered proteins

Advancing research on ecosystem service bundles for comparative assessments and synthesis

Social-ecological interactions have been shown to generate interrelated and reoccurring sets of ecosystem services, also known as ecosystem service bundles. Given the potential utility of the bundles concept, along with the recent surge in interest it is timely to reflect on the concept, its current use and potential for the future. Based on our ecosystem service bundle experience, expertise, and ecosystem service bundle analyses, we have found critical elements for advancing the utility of ecosystem service bundle concept and deepening its impact in the future. In this paper we 1) examine the different conceptualizations of the ecosystem service bundle concept; 2) show the range of benefits of using a bundles approach; 3) explore key issues for improving research on ecosystem service bundles, including indicators, scale, and drivers and relationships between ecosystem services; and 4) outline priorities for the future by facilitating comparisons of ecosystem service bundle research