Analysis of a gene family for PDF-like peptides from Arabidopsis

Plant defensins are small, basic peptides that have a characteristic three-dimensional folding pattern which is stabilized by four disulfide bridges. We show here that Arabidopsis contains in addition to the proper plant defensins a group of 9 plant defensin-like (PdfL) genes. They are all expressed at low levels while GUS fusions of the promoters showed expression in most tissues with only minor differences. We produced two of the encoded peptides in E. coli and tested the antimicrobial activity in vitro. Both were highly active against fungi but had lower activity against bacteria. At higher concentrations hyperbranching and swollen tips, which are indicative of antimicrobial activity, were induced in Fusarium graminearum by both peptides. Overexpression lines for most PdfL genes were produced using the 35S CaMV promoter to study their possible in planta function. With the exception of PdfL4.1 these lines had enhanced resistance against F. oxysporum. All PDFL peptides were also transiently expressed in Nicotiana benthamiana leaves with agroinfiltration using the pPZP3425 vector. In case of PDFL1.4 this resulted in complete death of the infiltrated tissues after 7 days. All other PDFLs resulted only in various degrees of small necrotic lesions. In conclusion, our results show that at least some of the PdfL genes could function in plant resistance.

The lectin LecA sensitizes the human stretch-activated channel TREK-1 but not Piezo1 and binds selectively to cardiac non-myocytes

Funding Acknowledgements

Type of funding sources: Public grant(s) – EU funding. Main funding source(s): This research was supported by the European Research Council (Advanced Grant CardioNECT, Project ID: #323099, PK) and a research grant from the Ministry of Science, Research and Arts Baden-Württemberg (MWK-BW Sonderlinie Medizin, #3091311631).

Mechanical stimuli are detected and transduced by cellular mechano-sensors, including stretch-activated ion channels (SAC). SAC are activated by stretch and changes in membrane curvature but their precise role in the heart is unclear.

The lectin LecA is a virulence factor of Pseudomonas aeruginosa and essential for bacterial cell invasion by inducing membrane curvature. We investigate whether LecA modulates SAC activity, namely TREK-1 and Piezo1 in human embryonic kidney (HEK) cells.

Confocal microscopy and electron tomography were used to follow binding dynamics of LecA, and the ion channel activity was recorded using the patch-clamp technique. Additionally, freshly isolated cardiac cells were used for studies into cell type dependency of LecA binding.

LecA binds within seconds to cell surface. Local plasma membrane invaginations are detected by 17 min of LecA exposure. LecA sensitizes TREK-1, but not Piezo1, to voltage and mechanical stimulation. In freshly isolated cardiac cells, LecA binds to non-myocytes, but not to cardiomyocytes from mouse, rabbit, pig, and human.

Our results suggest that LecA may serve as a pharmacological tool to study cardiac SAC in a cell type-preferential manner. Abstract Figure. Graphical abstract

[Steered Molecular Dynamics Simulation Study of Quantified Effects of Point Mutation Induced by Breast Cancer on Mechanical Behavior of E-Cadherin]

E-cadherin is a member of the cadherin family that plays a key role in the formation of cell-cell adhesion among epithelial tissues. Point mutations are one of the structural abnormalities of E-cadherin in human carcinomas. Such abnormalities can alter mechanical properties of proteins that play an important role in their biological activities. To determine the impact of point mutations on protein mechanical properties, the second fragment of extracellular domain of E-cadherin was modeled using steered molecular dynamics simulations. The molecular dynamics modeling included application of tensile forces in both constant velocity and constant force modes to examine the effects of Met282 to He and Asn315 to Ser mutations on mechanical behavior of protein structure. The stabilities of the wild type and mutant structures were also obtained by the protein design foldX algorithm. Results confirmed the lower stability of the mutant domains compared to the wild type. The mutated proteins displayed softer behavior than the reference protein and their stiffness decreased by up to 34%. Our findings suggest that local changes in molecular structure due to mutations may lead to noticeable alterations in mechanical properties within the entire domain. Since the function of protein is related to its structure, these changes may influence the function of the protein.