Towards designing a synthetic antituberculosis vaccine: The Rv3587c peptide inhibits mycobacterial entry to host cells.

Mycobacterium tuberculosis is considered one of the most successful pathogens in the history of mankind, having caused 1.7 million deaths in 2016. The amount of resistant and extensively resistant strains has increased; BCG has been the only vaccine to be produced in more than 100 years though it is still unable to prevent the disease's most disseminated form in adults; pulmonary tuberculosis. The search is thus still on-going for candidate antigens for an antituberculosis vaccine. This paper reports the use of a logical and rational methodology for finding such antigens, this time as peptides derived from the Rv3587c membrane protein. Bioinformatics tools were used for predicting mycobacterial surface location and Rv3587c protein structure whilst circular dichroism was used for determining its peptides' secondary structure. Receptor-ligand assays identified 4 high activity binding peptides (HABPs) binding specifically to A549 alveolar epithelial cells and U937 monocyte-derived macrophages, covering the region between amino acids 116 and 193. Their capability for inhibiting Mtb H37Rv invasion was evaluated. The recognition of antibodies from individuals suffering active and latent tuberculosis and from healthy individuals was observed in HABPs capable of avoiding mycobacterial entry to host cells. The results showed that 8 HABPs inhibited such invasion, two of them being common for both cell lines: 39265 (155VLAAYVYSLDNKRLWSNLDT173) and 39266 (174APSNETLVKTFSPGEQVTTY192). Peptide 39265 was the least recognised by antibodies from the individuals' sera evaluated in each group. According to the model proposed by FIDIC regarding synthetic vaccine development, peptide 39265 has become a candidate antigen for an antituberculosis vaccine.

Quantifying intracellular Mycobacterium tuberculosis: An essential issue for in vitro assays.

Many studies about intracellular microorganisms which are important regarding diseases affecting public health have been focused on the recognition of host-pathogen interactions, thereby ascertaining the mechanisms by which the pathogen invades a cell and makes it become its host. Such knowledge enables understanding the immunological response triggered by these interactions for obtaining useful information for developing vaccines and drugs. Quantitative cell infection assay protocols are indispensable regarding studies involving Mycobacterium tuberculosis, which takes the lives of more than 2 million people worldwide every year; however, sometimes these are limited by the pathogen's slow growth. Concerning such limitation, a detailed review is presented here regarding the different methods for quantifying and differentiating an intracellular pathogen, the importance of mycobacteria aggregate dissociation and multiplicity of infection (MOI) in infection assays. The methods' differences, advantages, and disadvantages are discussed regarding intra and extracellular bacteria (on cell surface) differentiation, current problems are outlined, as are the solutions provided using fluorophores and projections made concerning quantitative infection assays.

Cell-Peptide Specific Interaction Can Inhibit Mycobacterium tuberculosis H37Rv Infection.

Studying proteins from the M. tuberculosis H37Rv envelop is important for understanding host-pathogen interaction regarding bacterial infection and survival within a host; such knowledge is indispensable regarding studies aimed at developing drugs or vaccines against tuberculosis, a disease which continues to cause more than one million deaths worldwide every year. The present work presents a study of the Rv3705c protein which has been described as being an outer protein. Several servers and bioinformatics' tools were used for predicting its location on mycobacterial surface and a 3D model of the protein was obtained which was then compared to experimental circular dichroism results for its peptides. PCR assays were used for corroborating rv3705c gene presence and transcription in a laboratory strain and immunoblotting and electron microscopy were used for confirming protein localisation on cell envelop. Receptor-ligand assays revealed two peptides having high specific binding (HABPs); peptide 38485 ((121)DRAFHRVVDRTVGTSGQTTA(140)) bound to both cell lines used as infection target (U937 and A549 epithelial cell line-derived macrophages) and 38488 ((181)RLRENVLLQAKVTQSGNAGP(200)) bound to U937 cells. It was found that peptide 38485 provided significant inhibition regarding mycobacterial entry to both cell lines in in vitro assays. These results led to proposing peptide 38485 as one of the epitopes to be used in future studies aimed at characterising the immune response of functionally important synthetic peptides which could be included in developing a synthetic anti-tuberculosis vaccine.

Mce4F Mycobacterium tuberculosis protein peptides can inhibit invasion of human cell lines.

This work was aimed at studying the Mycobacterium tuberculosis H37Rv Rv3494c protein, taking into account that it belongs to the mammalian cell entry family (mce) which is thought to have important functions in the disease's pathogenesis. The protein was characterized in silico; its presence on mycobacterial surface was confirmed by immunoelectron microscopy. High-activity binding peptides (HABPs) were identified by binding assays with (125)I; their ability to inhibit mycobacterial entry to two cell lines (U937 alveolar macrophages and A549 epithelial cells) was ascertained and their role in bacterial entry was confirmed by fluorescent microsphere internalization assay. This protein's predicted alpha-helix structure was confirmed by circular dichroism of its peptides. All HABPs inhibited mycobacterial entry to cells and that the 38379 peptide ((201)IDQAGPFLQAQIRAGGDIKSY(220)) had high binding ability and inhibited the mycobacterial entry to both cell lines assayed here. Rv3494c peptides 38370 ((21)LSVMAIFYLRLPATFGIGTY(40)), 38373 ((81)HMRLNSGTAIPSNVTATVRSY(100)) and 38379 ((201)IDQAGPFLQAQIRAGGDIKSY(220)) showed to be HABP and inhibited mycobacterial entry to A549 cells and peptide 38382 ((261)RPSFPALAASLANLGRVGVIY(280)) bind to U937 and inhibited the mycobacterial entry to this cell line; all of these sequences play an important role in cell line recognition and invasion, and may thus be considered in the search for prophylactic candidates against tuberculosis.

Rv1268c protein peptide inhibiting Mycobacterium tuberculosis H37Rv entry to target cells.

Tuberculosis (TB) remains one of the most worrying infectious diseases affecting public health around the world; 8.7 million new TB cases were reported in 2011. The search for an Mycobacterium tuberculosis H37Rv protein sequence which is functionally important in host-pathogen interaction has been proposed for developing a new vaccine which will allow efficient and safe control of the spread of this disease. The present study thus reports the results obtained for the Rv1268c protein described in the M. tuberculosis H37Rv genome as a hypothetical unknown, probably secreted, protein based on a highly robust, specific, sensitive and functional approach to the search for potential epitopes to be included in an anti-tuberculosis vaccine. Rv1268c presence was determined by immunoblotting after obtaining polyclonal sera against mycobacterial total sonicate or subcellular fractions. Such sera were used in electron immunomicroscopy (EIM) for confirming protein localisation on the M. tuberculosis envelop by recognising colloidal gold-labelled immunoglobulin. Screening assays revealed the presence of two sequences having high binding activity: one binding A549 alveolar epithelial cells ((141)TGMAALEQYLGSGHAVIVSI(160)) and other binding U937 monocyte-derived macrophages ((21)AVALGLASPADAAAGTMYGD(40)). Such sequences' ability to inhibit mycobacterial entry during in vitro assays was analysed. The structure of synthetic peptides binding to target cells was also determined, bearing in mind the structure-function relationship. These results, together with those obtained for other proteins, have been involved in selecting peptides which might be included in a subunit-based anti-tuberculosis vaccine.