Different proposed applications of bacteriorhodopsin

Bacteriorhodopsin (BR) is an integral membrane protein found in "purple membrane" (the Archaea cell membrane) mainly in Halobacteria. This protein absorbs green light (wavelength 500-650 nm, with the absorption maximum at 568 nm) and converts it into an electrochemical gradient. This gradient in turn is used for ATP production. The ability of BR to convert light energy into chemical energy or sunlight into electricity has been used in different applications mainly optical appliances but also for therapeutic/medical applications and research. This review surveys some of these applications that have been patented in the last five years.     

Dissecting the mechanism and assembly of a complex virulence mycobacterial lipid

Mycobacterium tuberculosis cell envelope is a treasure house of biologically active lipids of fascinating molecular architecture. Although genetic studies have alluded to an array of genes in biosynthesis of complex lipids, their mechanistic, structural, and biochemical principles have not been investigated. Here, we have dissected the molecular logic underlying the biosynthesis of a virulence lipid phthiocerol dimycocerosate (PDIM). Cell-free reconstitution studies demonstrate that polyketide synthases, which are usually involved in the biosynthesis of secondary metabolites, are responsible for generating complex lipids in mycobacteria. We show that PapA5 protein directly transfers the protein bound mycocerosic acid analogs on phthiocerol to catalyze the final esterification step. Based on precise identification of biological functions of proteins from Pps cluster, we have rationally produced a nonmethylated variant of mycocerosate esters. Apart from elucidating mechanisms that generate chemical heterogeneity with PDIMs, this study also presents an attractive approach to explore host-pathogen interactions by altering mycobacterial surface coat.     

Migration events play significant role in genetic differentiation: A microsatellite-based study on Sikkim settlers

Background  

A wide spectrum of genetic diversity in mongoloids of India is well documented. Though all mongoloids of India are known to have originated from the Mongol region of China but the period and route of migration from their native land to different Himalayan regions is little known. Thus the studies on genomic diversity of people of Sikkim, a central Himalayan state of India with different migrant mongoloid groups, assume great significance in understanding the impact of migratory events in the genetic differentiation of populations. We therefore studied the genetic diversity on the basis of 13-tetra nucleotide and 2 penta nucleotide microsatellite loci for a total of 208 allele frequencies in three major populations of Sikkim, with different ethno history and time of settlement.     

The effect of body mass index on global brain volume in middle-aged adults: a cross sectional study

Background  

Obesity causes or exacerbates a host of medical conditions, including cardiovascular, pulmonary, and endocrine diseases. Recently obesity in elderly women was associated with greater risk of dementia, white matter ischemic changes, and greater brain atrophy. The purpose of this study was to determine whether body type affects global brain volume, a marker of atrophy, in middle-aged men and women.     

Photochromicity of Anabaena sensory rhodopsin, an atypical microbial receptor with a cis-retinal light-adapted form

We characterize changes in isomeric states of the retinylidene chromophore during light-dark adaptation and photochemical reactions of Anabaena (Nostoc) sp. PCC7120 sensory rhodopsin (ASR). The results show that ASR represents a new type of microbial rhodopsin with a number of unusual characteristics. The three most striking are: (i) a primarily all-trans configuration of retinal in the dark-adapted state and (ii) a primarily 13-cis light-adapted state with a blue-shifted and lower extinction absorption spectrum, opposite of the case of bacteriorhodopsin; and (iii) efficient reversible light-induced interconversion between the 13-cis and all-trans unphotolyzed states of the pigment. The relative amount of ASR with cis and trans chromophore forms depends on the wavelength of illumination, providing a mechanism for single-pigment color sensing analogous to that of phytochrome pigments. In addition ASR exhibits unusually slow formation of L-like and M-like intermediates, with a dominant accumulation of M during the photocycle. Co-expression of ASR with its putative cytoplasmic transducer protein shifts the absorption maximum and strongly decreases the rate of dark adaptation of ASR, confirming interaction between the two proteins. Thus ASR, the first non-haloarchaeal sensory rhodopsin characterized, demonstrates the diversity of photochemistry of microbial rhodopsins. Its photochromic properties and the position of its two ground state absorption maxima suggest it as a candidate for controlling differential photosynthetic light-harvesting pigment synthesis (chromatic adaptation) or other color-sensitive physiological responses in Anabaena cells.     

Comparison of simple sequence repeats in 19 Archaea

All organisms that have been studied until now have been found to have differential distribution of simple sequence repeats (SSRs), with more SSRs in intergenic than in coding sequences. SSR distribution was investigated in Archaea genomes where complete chromosome sequences of 19 Archaea were analyzed with the program SPUTNIK to find di- to penta-nucleotide repeats. The number of repeats was determined for the complete chromosome sequences and for the coding and non-coding sequences. Different from what has been found for other groups of organisms, there is an abundance of SSRs in coding regions of the genome of some Archaea. Dinucleotide repeats were rare and CG repeats were found in only two Archaea. In general, trinucleotide repeats are the most abundant SSR motifs; however, pentanucleotide repeats are abundant in some Archaea. Some of the tetranucleotide and pentanucleotide repeat motifs are organism specific. In general, repeats are short and CG-rich repeats are present in Archaea having a CG-rich genome. Among the 19 Archaea, SSR density was not correlated with genome size or with optimum growth temperature. Pentanucleotide density had an inverse correlation with the CG content of the genome.