Cryo-EM research in India.

To celebrate the 50th anniversary of Cell Press and the Cell special issue focusing on structural biology, we want to highlight the rapid progress of cryo-EM related research in India in this collection of Voices. We have asked structural biologists to introduce their research and the national cryo-EM facilities throughout the country.

and human hexokinases share similar active sites but display distinct quaternary architectures.

Malaria is a devastating disease caused by a protozoan parasite. It affects over 300 million individuals and results in over 400 000 deaths annually, most of whom are young children under the age of five. Hexokinase, the first enzyme in glucose metabolism, plays an important role in the infection process and represents a promising target for therapeutic intervention.

βγ-Crystallination Endows a Novel Bacterial Glycoside Hydrolase 64 with Ca-Dependent Activity Modulation.

The prokaryotic βγ-crystallins are a large group of uncharacterized domains with Ca-binding motifs. We have observed that a vast number of these domains are found appended to other domains, in particular, the carbohydrate-active enzyme (CAZy) domains. To elucidate the functional significance of these prospective Ca sensors in bacteria and this widespread domain association, we have studied one typical example from , a bacterium known for its ability to produce acetone, butanol, and ethanol through fermentation of several carbohydrates.

Interface interactions between βγ-crystallin domain and Ig-like domain render Ca -binding site inoperative in abundant perithecial protein of Neurospora crassa.

We describe a set of proteins in which a βγ-crystallin domain pairs with an Ig-like domain, and which are confined to microbes, like bacteria, slime molds and fungi. DdCAD-1 (Ca -dependent cell adhesion molecule-1) and abundant perithecial protein (APP) represent this class of molecules. Using the crystal structure of APP-NTD (N-terminal domain of APP), we describe its mode of Ca binding and provide a generalized theme for correct identification of the Ca -binding site within this class of molecules.

A Transition Metal-Binding, Trimeric βγ-Crystallin from Methane-Producing Thermophilic Archaea, Methanosaeta thermophila.

βγ-Crystallins are important constituents of the vertebrate eye lens, whereas in microbes, they are prevalent as Ca-binding proteins. In archaea, βγ-crystallins are conspicuously confined to two methanogens, viz., Methanosaeta and Methanosarcina.

Microbial βγ-crystallins.

βγ-Crystallins have emerged as a superfamily of structurally homologous proteins with representatives across the domains of life. A major portion of this superfamily is constituted by members from microorganisms. This superfamily has also been recognized as a novel group of Ca(2+)-binding proteins with huge diversity.

Ca2+-binding motif of βγ-crystallins.

βγ-Crystallin-type double clamp (N/D)(N/D)XX(S/T)S motif is an established but sparsely investigated motif for Ca(2+) binding. A βγ-crystallin domain is formed of two Greek key motifs, accommodating two Ca(2+)-binding sites. βγ-Crystallins make a separate class of Ca(2+)-binding proteins (CaBP), apparently a major group of CaBP in bacteria.

Aggregation-prone near-native intermediate formation during unfolding of a structurally similar nonlenticular βγ-crystallin domain.

The folding and unfolding of structurally similar proteins belonging to a family have long been a focus of investigation of the structure-(un)folding relationship. Such studies are yet to reach a consensus about whether structurally similar domains follow common or different unfolding pathways. Members of the βγ-crystallin superfamily, which consists of structurally similar proteins with limited sequence similarity from diverse life forms spanning microbes to mammals, form an appropriate model system for exploring this relationship further.

Decoding the molecular design principles underlying Ca(2+) binding to βγ-crystallin motifs.

Numerous proteins belonging to the recently expanded βγ-crystallin superfamily bind Ca(2+) at the double-clamp N/D-N/D-X(1)-X(2)-S/T-S motif. However, there have been no attempts to understand the intricacies involving Ca(2+) binding, such as the determinants of Ca(2+)-binding affinity and their contributions to gain in stability. This work is an in-depth analysis of understanding the modes and determinants of Ca(2+) binding to βγ-crystallin motifs.