Evolutionary journey of the Gc protein (vitamin D-binding protein) across vertebrates
With so many diverse functions such as transporter of vitamin D metabolites and fatty acids, actin scavenger and macrophage activating factor, Gc must have been one of the most conserved proteins in animal kingdom. Our objective was to investigate the evolution of Gc by analyzing its differences at protein level. Using BLAST (Basic Local Alignment Search Tool) searches, Gc amino acid sequences were analyzed for homology. Clustal W2 and Jalview were used for multiple sequence alignment analysis, phylogenetic tree by PhyML 3.0 while Batch Web CD-Search Tool was used for identification for conserved domains within protein sequences. Gc protein percent identity between human and rabbit was 83%, which decreased to 81% with cow, 78% with mouse, 76% with rat, 51% with chicken, 41% with frog and 28% with zebrafish. Phylogram showed that rat Gc was the most diverged, while chicken Gc was the most conserved protein. Analysis also indicated high homology among mammals (human, rabbit, cow, rat, and mouse). Gc is a highly conserved protein in chicken and zebrafish. However, the distance from ancestral protein gradually increased in amphibian (frog) and mammals (human, rabbit, cow, rat, and mouse). Human Gc and rabbit Gc appear to be recently evolved proteins. There appears to be an interesting evolutionary pattern- chicken Gc has the least distance from the ancestral protein, while rat Gc is the most diverged. There is no vertebrate devoid of Gc which is suggestive of its important role in vitamin D metabolism in vertebrates.
A NAD(P) reductase like protein is the salicylic acid receptor in the appendix of the Sauromatum guttatum inflorescence
The mode of action of the thermogenic inducers (salicylic acid, aspirin, and 2,6-dihydroxybenzoic acid) in the appendix of the Sauromatum guttatum inflorescence is poorly understood. Using ESI-MS and light scattering analysis, we have demonstrated that NAD(P) reductase like protein (RL) is the salicylic acid receptor in the Sauromatum appendix. RL was self-assembled in water into a large unit with a hydrodynamic diameter of 800 nm. In the presence of 1 pM salicylic acid, RL exhibited discontinuous and reversible volume phase transitions. The phase volume changed from 800 to 300 nm diameter and vice versa. RL stayed at each phase volume for ~4–5 min with a fast relaxation time between the 2 phases. ESI-MS analysis of RL extracted from appendices treated with salicylic acid, aspirin, and 2,6-DHBA at a micromolar range demonstrated that these compounds are capable of inducing graded conformational changes that are concentration-dependent. A strong correlation between RL conformations and heat-production induced by salicylic acid was also observed. These preliminary findings reveal structural and conformational roles for RL by which plants regulate their temperature and synchronize their time keeping mechanisms.
Multiple fuzzy interactions in the moonlighting function of thymosin-β4
Thymosine β4 (Tß4) is a 43 amino acid long intrinsically disordered protein (IDP), which was initially identified as an actin-binding and sequestering molecule. Later it was described to have multiple other functions, such as regulation of endothelial cell differentiation, blood vessel formation, wound repair, cardiac cell migration, and survival.1 The various functions of Tβ4 are mediated by interactions with distinct and structurally unrelated partners, such as PINCH, ILK, and stabilin-2, besides the originally identified G-actin. Although the cellular readout of these interactions and the formation of these complexes have been thoroughly described, no attempt was made to study these interactions in detail, and to elucidate the thermodynamic, kinetic, and structural underpinning of this range of moonlighting functions. Because Tβ4 is mostly disordered, and its 4 described partners are structurally unrelated (the CTD of stabilin-2 is actually fully disordered), it occurred to us that this system might be ideal to characterize the structural adaptability and ensuing moonlighting functions of IDPs. Unexpectedly, we found that Tβ4 engages in multiple weak, transient, and fuzzy interactions, i.e., it is capable of mediating distinct yet specific interactions without adapting stable folded structures.
SS-map: Visualizing cooperative secondary structure elements in protein ensembles
We present SS-map, a tool to visualize the secondary structure content of ensembles of proteins. When generating ensembles of intrinsically disordered proteins, we lose the understanding a single native structure gives for folded proteins. It then becomes difficult to visualize the composition of the ensembles or to detect transient helices such as MoRFs. Conformational propensities for single residues also hide the nature of cooperative structures. Here we show how SS-map describes folded and unfolded ensembles of some peptides and gives a new view of the ensembles used to describe intrinsically disordered proteins with residual structure in computational and NMR experiments. This tool is implemented in an open-source python code located at code.google.com/p/ss-map
Functional fragments of disorder in outer membrane β barrel proteins
The traditional view of “sequence–structure–function” has been amended by the discovery of intrinsically disordered proteins. Almost 50% of PDB structures are now known to have one or more regions of disorder, which are involved in diverse functions. These regions typically possess low aromatic content and sequence complexity as well as high net charge and flexibility. In this study, we examined the composition and contribution of intrinsic disorder in outer membrane β barrel protein functions. Our systematic analysis to find the dual personality (DP) fragments, which often function by disorder–order transitions, revealed the presence of 61 DP fragments with 234 residues in β barrel trans membrane protein structures. It was found that though the disorder is more prevalent in the periplasmic regions, most of the residues which undergo disorder–order transitions are found in the extracellular regions. For example, the calcium binding sites in BtuB protein are found to undergo disorder to order transition upon binding calcium. The conformational change in the cell receptor binding site of the OpcA protein, which is important in host cell interactions of N. meningitidis, was also found to be due to the disorder–order transitions occurring in the presence of the ligand. The natively disordered nature of DP fragments makes it more appropriate to call them “functional fragments of disorder.” The present study provides insight into the roles played by intrinsically disordered regions in outer membrane protein functions.
Structural characterizations of phosphorylatable residues in transmembrane proteins from Arabidopsis thaliana
Phosphorylation is a common post-translational modification that plays important roles in a wide range of biochemical and cellular processes. Many enzymes and receptors can be switched “on” or “off” by conformational changes induced by phosphorylation. The phosphorylation process is mediated by a family of enzymes called kinase. Currently, more than 1,000 different kinases have been identified in Arabidopsis thaliana proteome. Kinases interact with each other and with many regulatory proteins forming phosphorylation networks. These phosphorylation networks modulate the signaling processes and control the functions of cells. Normally, kinases phosphorylate serines, threonines, and tyrosines. However, in many proteins, not all of these 3 types of amino acids can be phosphorylated. Therefore, identifying the phosphorylation sites and the possible phosphorylation events is very important in decoding the processes of regulation and the function of phosphorylation networks. In this study, we applied computational and bioinformatics tools to characterize the association between phosphorylation events and structural properties of corresponding proteins by analyzing more than 50 trans-membrane proteins from Arabidopsis thaliana. In addition to the previously established conclusion that phosphorylation sites are closely associated with intrinsic disorder, we found that the phosphorylation process may also be affected by solvent accessibility of phosphorylation sites and further promoted by neighboring modification events.