Saturation Mutagenesis of the Transmembrane Region of HokC in Escherichia coli Reveals Its High Tolerance to Mutations.

Cells adapt to different stress conditions, such as the antibiotics presence. This adaptation sometimes is achieved by changing relevant protein positions, of which the mutability is limited by structural constrains. Understanding the basis of these constrains represent an important challenge for both basic science and potential biotechnological applications. To study these constraints, we performed a systematic saturation mutagenesis of the transmembrane region of HokC, a toxin used by Escherichia coli to control its own population, and observed that 92% of single-point mutations are tolerated and that all the non-tolerated mutations have compensatory mutations that reverse their effect. We provide experimental evidence that HokC accumulates multiple compensatory mutations that are found as correlated mutations in the HokC family multiple sequence alignment. In agreement with these observations, transmembrane proteins show higher probability to present correlated mutations and are less densely packed locally than globular proteins; previous mutagenesis results on transmembrane proteins further support our observations on the high tolerability to mutations of transmembrane regions of proteins. Thus, our experimental results reveal the HokC transmembrane region high tolerance to loss-of-function mutations that is associated with low sequence conservation and high rate of correlated mutations in the HokC family sequences alignment, which are features shared with other transmembrane proteins.

Cell penetrating peptides and cationic antibacterial peptides: two sides of the same coin.

Cell penetrating peptides (CPP) and cationic antibacterial peptides (CAP) have similar physicochemical properties and yet it is not understood how such similar peptides display different activities. To address this question, we used Iztli peptide 1 (IP-1) because it has both CPP and CAP activities. Combining experimental and computational modeling of the internalization of IP-1, we show it is not internalized by receptor-mediated endocytosis, yet it permeates into many different cell types, including fungi and human cells. We also show that IP-1 makes pores in the presence of high electrical potential at the membrane, such as those found in bacteria and mitochondria. These results provide the basis to understand the functional redundancy of CPPs and CAPs.

Moonlighting peptides with emerging function.

Hunter-killer peptides combine two activities in a single polypeptide that work in an independent fashion like many other multi-functional, multi-domain proteins. We hypothesize that emergent functions may result from the combination of two or more activities in a single protein domain and that could be a mechanism selected in nature to form moonlighting proteins. We designed moonlighting peptides using the two mechanisms proposed to be involved in the evolution of such molecules (i.e., to mutate non-functional residues and the use of natively unfolded peptides). We observed that our moonlighting peptides exhibited two activities that together rendered a new function that induces cell death in yeast. Thus, we propose that moonlighting in proteins promotes emergent properties providing a further level of complexity in living organisms so far unappreciated.

Detección del papilomavirus humano en ADN de tejido normal y lesiones premalignas del cérvix por hibridación molecular / Identification of human papilloma virus in DNA of normal tissue and precursor lesions of uterine cervix by molecular hybridization

Se analizaron 64 muestras de ADN obtenido de tejido histológicamente normal del cérvix y de lesiones tempranas del cáncer cervical por hibridación dot-blot, para detectar la presencia de papilomavirus humano(PVH). Utilizando ADN de controles adecuados y sondas específicas, detectamos la infección por PVH en 39 por ciento(25 de 64) de los casos; mientras que 61 por ciento (39 de 64) resultó negativo a PVH. Se detectó PVH del grupo de ®bajo riesgo¼ (tipo 6/11) en un 80 por ciento (20 de 25) de las muestras de ADN; mientras que un 8 por ciento (2 de 25) fue positivo a PVH del grupo de ®alto riesgo¼ (tipo 16/18). Además, encontramos 12 por ciento (3 de 25) de las muestras positivas a ambos grupos de virus