Seema Joshi

Interaction studies of novel cell selective antimicrobial peptides with model membranes and E. coli ATCC 11775

Cationic antimicrobial peptides (CAMPs) are novel candidates for drug development. Here we describe design of six short and potent CAMPs (SA-1 to SA-6) based on a minimalist template of 12 residues H+HHG+HH+HH+NH2 (where H: hydrophobic amino acid and +: charged hydrophilic amino acid). Designed peptides exhibit good antibacterial activity in micro molar concentration range (1-32 mug/ml) and rapid clearance of Gram-positive and Gram-negative bacterial strains at concentrations higher than MIC. For elucidating mode of action of designed peptides various biophysical studies including CD and Trp fluorescence were performed using model membranes. Further based on activity, selectivity and membrane bound structure; modes of action of Trp rich peptide SA-3 and template based peptide SA-4 were compared. Calcein dye leakage and transmission electron microscopic studies with model membranes exhibited selective membrane active mode of action for peptide SA-3 and SA-4. Extending our work from model membranes to intact E. coli ATCC 11775 in scanning electron micrographs we could visualize different patterns of surface perturbation caused by peptide SA-3 and SA-4. Further at low concentration rapid translocation of FITC-tagged peptide SA-3 into the cytoplasm of E. coli cells without concomitant membrane perturbation indicates involvement of intracellular targeting mechanism as an alternate mode of action as was also evidenced in DNA retardation assay. For peptide SA-4 concentration dependent translocation into the bacterial cytoplasm along with membrane perturbation was observed. Establishment of a non specific membrane lytic mode of action of these peptides makes them suitable candidates for drug development.

Nonprocessive [2 + 2]e- off-loading reductase domains from mycobacterial nonribosomal peptide synthetases.

In mycobacteria, polyketide synthases and nonribosomal peptide synthetases (NRPSs) produce complex lipidic metabolites by using a thio-template mechanism of catalysis. In this study, we demonstrate that off-loading reductase (R) domain of mycobacterial NRPSs performs two consecutive [2 + 2]e- reductions to release thioester-bound lipopeptides as corresponding alcohols, using a nonprocessive mechanism of catalysis. The first crystal structure of an R domain from Mycobacterium tuberculosis NRPS provides strong support to this mechanistic model and suggests that the displacement of intermediate would be required for cofactor recycling. We show that 4e- reductases produce alcohols through a committed aldehyde intermediate, and the reduction of this intermediate is at least 10 times more efficient than the thioester-substrate. Structural and biochemical studies also provide evidence for the conformational changes associated with the reductive cycle. Further, we show that the large substrate-binding pocket with a hydrophobic platform accounts for the remarkable substrate promiscuity of these domains. Our studies present an elegant example of the recruitment of a canonical short-chain dehydrogenase/reductase family member as an off-loading domain in the context of assembly-line enzymology.

Synthesis, antimicrobial activity and structure-activity relationship study of N,N-dibenzyl-cyclohexane-1,2-diamine derivatives.

We report herein synthesis and antimicrobial activity of a series of N,N-dibenzyl-cyclohexane-1,2-diamine derivatives. In order to study the structure-activity relationship of substituted dibenzyl-cyclohexane-1,2-diamine derivatives, 44 structurally diverse compounds were synthesized and tested against Gram-positive and Gram-negative bacterial strains. Among them, compounds 17-20, 26, 37, 38 were found to be more active than tetracycline with MIC value ranging 0.0005-0.032xa0μg/mL and no hemolysis upto 1024xa0μg/mL in mammalian erythrocytes was observed. Some of the compounds have also shown very promising antifungal activity against Candida albicans, Candida glabrata and Geotrichum candidium.

Synthesis and antibacterial activity of benzyl-[3-(benzylamino-methyl)-cyclohexylmethyl]-amine derivatives

A series of benzyl-[3-(benzylamino-methyl)-cyclohexylmethyl]-amine derivatives with different substitution pattern on the aromatic ring have been prepared and evaluated for their antibacterial activity against Gram-positive and Gram-negative bacterial strains. Most of the compounds exhibit potent activity against Pseudomonas aeruginosa and Staphylococcus epidermidis while compounds 6l and 6m showed antibacterial activity against all the four bacterial strains with MIC values ranging from 0.002 to 0.016 microg/mL and no hemolytic activity up to 512 microg/mL in mammalian erythrocytes was observed.

Comparative mode of action of novel hybrid peptide CS-1a and its rearranged amphipathic analogue CS-2a

Cell selective, naturally occurring, host defence cationic peptides present a good template for the design of novel peptides with the aim of achieving a short length with improved antimicrobial potency and selectivity. A novel, short peptide CS‐1a (14 residues) was derived using a sequence hybridization approach on sarcotoxin I (39 residues) and cecropin B (35 residues). The sequence of CS‐1a was rearranged to enhance amphipathicity with the help of a Schiffer–Edmundson diagram to obtain CS‐2a. Both peptides showed good antibacterial activity in the concentration range 4–16 μg·mL−1 against susceptible as well as drug‐resistant bacterial strains, including the clinically relevant pathogens Acenatobacter sp. and methicillin‐resistant Staphylococcus aureus. The major thrust of these peptides is their nonhaemolytic activity against human red blood cells up to a high concentration of 512 μg·mL−1. Compared to CS‐1a, amphipathic peptide CS‐2a showed a more pronounced α‐helical conformation, along with a better membrane insertion depth in bacterial mimic 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphocholine/1,2‐dipalmitoyl‐sn‐glycero‐3‐phospho‐(1′‐rac‐glycerol) small unilamellar vesicles. With equivalent lipid‐binding affinity, the two peptides assumed different pathways of membrane disruption, as demonstrated by calcein leakage and the results of transmission electron microscopy on model bacterial mimic large unilamellar vesicles. Extending the work from model membranes to intact Escherichia coli cells, differences in membrane perturbation were visible in microscopic images of peptide‐treated E. coli. The present study describes two novel short peptides with potent activity, cell selectivity and divergent modes of action that will aid in the future design of peptides with better therapeutic potential.

Synthesis and Antitubercular Activity Evaluation of Novel Unsymmetrical Cyclohexane-1,2-diamine Derivatives

A library of unsymmetrical cyclohexane‐1,2‐diamine derivatives were synthesized and evaluated for their activity against Mycobacterium tuberculosis H37Rv in vitro. Out of the 46 compounds synthesized, eight compounds (11h, 13a, 13e, 13f, 14a, 14c, 14d, and 15d) were found to be active at or below 6.25u2009µM concentration, with negligible toxicity to human red blood cells at a concentration much higher than the MIC99. Compound 13a was the best active compound showing inhibition at 3.125–6.25u2009µM, and was found to be non‐hemolytic up to 500u2009µg/mL concentration.

From the ‘Hindu rate of growth’ to ‘unstoppable India’: has the services sector played a role?

India shifted from an import substitution growth strategy (ISS) to an export-led-growth strategy (ELGS) in July 1991. Consequently, liberalisation was promulgated not only in the industrial sector but in the services sector too in the post-1991 period. ‘services-led-growth strategy’ – a concomitant of ELGS – has led to an improvement in the revealed comparative advantage in the export of commercial services during the period 1990–2005. Furthermore, the openness of services and foreign direct investment in services have emerged as important determinants of gross domestic product growth during the period 1995–2005. The author therefore argues that if ISS led to the ‘Hindu rate of growth’ in the first three decades of planning, it is the services-led growth which has made ‘India unstoppable’ on the economic front.

Antimicrobial activity and mode of action of novel, N-terminal tagged tetra-peptidomimetics

We report herein, synthesis and mode of action of novel, cell selective, N-terminal tagged tetra-peptide conjugates. Analogues AP1 and AP2 with linoleic acid and p-terphenyl carboxylic acid tagging showed potent activity against Gram-positive and Gram-negative bacterial strains including the clinically relevant pathogen MRSA. For active analogues interaction studies with model bacterial mimic membranes revealed a direct correlation between activity and membrane perturbation. Further, active conjugates showed membrane depolarization and severe bacterial membrane disrupting ability. The hydrophobic–charge–hydrophobic template designed here can be useful in further optimizing end tagged peptidomimetics for therapeutic potential.

Can IT and ITES bE an EngInE of growTh for IndIa: an EmpIrICal analySIS

India emerged as one of the fastest growing economies of the world during the 1990s because of the spectacular dynamism shown by the services sector. India’s services sector has been burgeoning fast and one of the major driver’s of the growth of services sector is Information Technology (IT) and Information Technol ogy Enabled Services (ITES). It is well documented in literature that IT impacts growth by different channels. In this study we try to empirically verify the question: Can IT and ITES be an engine of growth? Using micro‐level data of 100 households of 20 IT and ITES firms along with secondary data we tried to estimate the extent of indirect employment generation at macro‐level and the share of IT and ITES in total employment and total value added. According to our study, one job for skilled professional employed in IT and ITES spins off jobs for 0.48 semi‐skilled, low skills or unskilled workers. As per our estimates, the 16 lakh workers who are expected to be directly employed in IT sector in the FY 2008 would generate secondary em ployment for 7,68,000 people which would constitute 0.16 per cent of total employment. However, the share of consumption expenditure of 16 lakh professionals would be 20 per cent of total value added. Assuming the consumption expenditure of the IT and ITES workers and total value added to be the same/constant when we tried to assess the contribution of consumption expenditure of 2.3 million workers (who are projected to be directly absorbed by IT sector by 2010, NASSCOM, 2005) to total value added it comes out to be 29 per cent of total value added. The study says that the proportion of IT‐ITES in total employment may be small but its contribution to total value added is still very high. Indeed IT and ITES can be an engine of growth in India’s economy by way of generating demand impulses in the economy as has been hypothesised and shown through the present study. Keeping in view the contributions of this sector and its huge untapped potential as evident from the present study and various other studies, there is a need for introduction and implementation of policy initiatives to address the challenges faced by this sector and to sustain the growth driven by the services sector.

Service sector statistics in India: problems and way forward

– It has been observed in various studies that the “servicization” of the structures of production and employment has taken place in India. However, a problem peculiar to this sector or several types of services is that the output of some components of this sector is difficult to measure as well as to value it in monetary terms. The purpose of this paper is to identify the problems encountered in the measurement of service sector output. , – The paper makes use of secondary sources of data including various reports, books and journals, etc. An attempt has been made in this paper to review those studies which deal with measurement problems in services sector output. , – In the Indian context, it has been found that the data base on the service sector is highly disorganized. It has been recognized in studies that the limitation of the existing system is marred by the absence of a well-organized mechanism for maintaining a regular and proper database for this sector. A large number of the unorganized units are located in the service sector and the composition of units in the domain undergoes changes at a rapid pace because new units or newer service areas come into existence and others disappear with alarming frequency. Therefore, the need for “devising a proper classification of services” by identifying all new services and adopting a suitable methodology so as to maintain international comparability of data has been highlighted in various studies. , – Although there are studies which try to point out measurability problems of services in developed European economies, however, studies related to service sector statistics problems in India are far less in number. This paper will therefore mainly focus on the service sector statistics problems in India and point out the way forward.