We have open positions to undergrade, Master, PHD and Pos-Doc

Objectives

Our group has three main goals:

1. Functional and structural correlations between the homologues systems: Type II secretion system (T2SS) and the Type IV pilus (T4P) machineries.

2. Structural and Functional studies of the c-di-GMP signaling in the human pathogenic bacteria Leptospira interrogans serovar

3. Structural studies of the Type IV secretion system (T4SS).

Type II Secretion System (T2SS) and Type IV pilus  (T4P)

The type II secretion system is found in a wide range of bacteria as in all classes of Proteobacteria, in Chlamydia, Spirochetes and Cyanobacteria. The main role of the T2SS is to secrete proteins from the bacteria periplasm to the extracellular milieu to nutrient acquisition. Nevertheless, some exoproteins causes diseases, such as cholera toxin and some adhesins proteins. T2SS uses very sophisticated protein nanomachinery made by different protein complexes to translocate proteins from the cytoplasm to the extracellular environment. This nanomachinery has evolutionary relationship with the following systems: archaeal flagellum system; Type IV pilus (T4P) system; and transformation system in Gram positive. The T4P, that produces a bacterial cell-surface pilus structure, is involved in pathogenesis, cell motility such as twitching motility, and biofilm formation. We are interested in understanding the similarities and differences in the mechanism of function between T2SS and T4P.

 C-di-GMP Signaling in Leptospira interrogans

            Leptospirosis: Leptospira interrogans serovar Copenhageni is a human pathogen that causes leptospirosis, a worldwide zoonosis. About 10% of leptospiral infections may progress to multiple organ failure and pulmonary haemorrhages leading to death. As with many other bacterial pathogens, environmental changes are sensed by L. interrogans during the course of infection and may trigger transitions between different cellular states, such as biofilm formation and activation of pathogenicity mechanisms. Such transitions in bacteria are commonly regulated by intracellular levels of c-di-GMP and L. interrogans possesses a wide array of GGDEF family c-di-GMP producing enzymes, of EAL family c-di-GMP degradation enzymes, and a large number of c-di-GMP potential receptors. Those observations strongly suggest an important role of c-di-GMP signalling in the pathogenesis and in the biology of this spirochete.

             c-di-GMP bacterial signalling. Different forms of purine nucleotides have emerged as second messengers, including cyclic mononucleotides (cAMP and cGMP), cyclic dinucleotides (c-di-GMP, c-di-AMP and cAMP-GMP) and other linear nucleotides, (ppGpp and pppGpp). All of these have important roles in changing bacterial behaviour in response internal and external signals. A universal eubacterial mechanism of signal transduction mediated by the ubiquitous bacteria second messenger bis(3’→5′) cyclic GMP (c-di-GMP) controls various bacterial processes, such as biofilm production, bacterial adaptation to the external environment, production of virulence factors, and motility. This important cyclic dinucleotide is synthesized by GGDEF domains, which convert two molecules of GTP into one molecule of c-di-GMP and two molecules of pyrophosphate. The c-di-GMP molecule can be subsequently hydrolyzed to pGpG and GMP by specific phoshodiesterases (PDEs) that contain EAL and HD-GYP domains, respectively. Different protein and RNA classes have been described to be c-di-GMP receptors, as PilZ domains and riboswitches.

As c-di-GMP has been shown to play a central regulatory role in pathogenicity and virulence in microorganisms, the inhibition of c-di-GMP synthesis could be an interesting means to combat microbial diseases. Some studies have shown that c-di-GMP has ‘‘drug-like’’ properties to attenuate the virulence and pathogenesis and has a potential to be a novel therapeutic agent to prevent or treat cancer. c-di-GMP is an important signal to eucaryotic cells as a “danger-signal” and for this reason, it has immuno-modulatory and immunostimulatory properties making c-di-GMP molecule a potential vaccine adjuvant. The ability of some Leptospira species to grow in different conditions, such as in soil, water and in various mammalian organs and the bloodstream, suggests that the bacteria should possess different signaling pathways to sense the external environment and modulate an intracellular response in order to appropriately modify bacterial biochemistry, physiology and behavior. Therefore, we can expect that c-di-GMP will have an important role in Leptospira pathogenesis and in its life cycle. Since almost nothing is known about c-di-GMP signaling in Leptospira, we are interested in studying the signaling networks involving c-di-GMP, as well as its involvement with virulence and pathogenicity.

Type IV Secretion System (T4SS)

T4SS is a sophisticated nanomachine widespread along gram positive and gram negative bacteria, and some archae. T4SS are used in conjugation, a process in which ssDNA are translocated from a recipient cell to a donor cell, but also during pathogenesis to translocate proteins such as toxins or protein effectors into humans and animals. Different functions of T4SS have been reported, the bacteria can use the T4SS for the following proposes: i: to translocate proteins and protein–DNA complexes through bacterial membranes to the extracellular milieu or directly into the other cells, ii: to secrete DNA and proteins to the extracellular environment instead of a recipient cell and, iii: uptake DNA in a process called transformation.

Associations between T4SS and disease is very well known as gastric ulcers caused by H. pylori, brucellosis caused by B. suis, and Legionnaire desease caused by L. pneumophila. A. tumefaciens uses T4SS to inject oncogenic DNA and proteins within cells plant, and B. pertussis uses T4SS machinery to secrets pertussis toxin. Through the process of conjugation, antibiotic resistance and toxic genes can propagate among pathogenic strains and thus, T4SSs are important targets to halt the spread of antibiotic resistance genes, a terrible threat to human health. At the moment, we are interested in solving the structure of the entire T4SS machinery as well as its components by structural approach.