ABSTRACT
Peptidoglycan (PG) sacculi surround the cytoplasmic membrane, maintaining cell integrity by withstanding internal turgor pressure. During cell growth, PG endopeptidases cleave the crosslinks of the fully closed sacculi, allowing for the incorporation of new glycan strands and expansion of the peptidoglycan mesh. Outer-membrane-anchored NlpI associates with hydrolases and synthases near PG synthesis complexes, facilitating spatially close PG hydrolysis. Here, we present the structure of adaptor NlpI in complex with the endopeptidase MepS, revealing atomic details of how NlpI recruits multiple MepS molecules and subsequently influences PG expansion. NlpI binding elicits a disorder-to-order transition in the intrinsically disordered N-terminal of MepS, concomitantly promoting the dimerization of monomeric MepS. This results in the alignment of two asymmetric MepS dimers respectively located on the two opposite sides of the dimerization interface of NlpI, thus enhancing MepS activity in PG hydrolysis. Notably, the protein level of MepS is primarily modulated by the tail-specific protease Prc, which is known to interact with NlpI. The structure of the Prc-NlpI-MepS complex demonstrates that NlpI brings together MepS and Prc, leading to the efficient MepS degradation by Prc. Collectively, our results provide structural insights into the NlpI-enabled avidity effect of cellular endopeptidases and NlpI-directed MepS degradation by Prc.
Subject(s)
Endopeptidases , Lipoproteins , Peptidoglycan , Peptidoglycan/metabolism , Endopeptidases/metabolism , Endopeptidases/chemistry , Lipoproteins/metabolism , Lipoproteins/chemistry , Protein Binding , Protein Multimerization , Bacterial Proteins/metabolism , Bacterial Proteins/chemistry , Models, Molecular , Crystallography, X-Ray , Hydrolysis , Escherichia coli/metabolismABSTRACT
BACKGROUND AND OBJECTIVES: Considering the pulse widths of picosecond and nanosecond lasers used in cutaneous laser surgery differ by approximately one order of magnitude, can nanosecond lasers produce the optical effect in human skin similar to laser-induced optical breakdown (LIOB) caused by picosecond lasers? METHODS: Cutaneous changes induced by a focused fractional nanosecond 1064-nm Nd:YAG laser were evaluated by VISIA-CR imaging, histological examination, and harmonic generation microscopy (HGM). RESULTS: A focused fractional nanosecond 1064-nm Nd:YAG laser can generate epidermal vacuoles or dermal cavities similar to the phenomenon of LIOB produced by picosecond lasers. The location and extent of photodisruption can be controlled by the laser fluence and focus depth. Moreover, laser-induced shock wave propagation and thermal degeneration of papillary collagen can be observed by HGM imaging. CONCLUSION: Focused fractional nanosecond lasers can produce an optical effect on human skin similar to LIOB caused by picosecond lasers. With techniques of application, the treatment can induce epidermal and dermal repair mechanisms in a tunable fashion to improve skin texture, wrinkles, scars, and dyspigmentation, without disrupting the epidermal surface.
Subject(s)
Lasers, Solid-State , Skin , Humans , Lasers, Solid-State/therapeutic use , Skin/radiation effects , Laser Therapy/methods , Laser Therapy/instrumentationABSTRACT
In this study, a multi-objective optimization of directed energy deposition (DED) process was conducted with Taguchi-Grey relational analysis. The used part was designed as a flat rectangle which would be deposited by a single-layer and multi-track DED process. Firstly, after finishing Taguchi experiments, the effects of five control factors (laser power, overlap ratio, powder feed rate, scanning speed and laser defocus distance) on three DED product qualities (cladding efficiency, surface roughness and porosity) were, respectively, analyzed. Then, through Grey relational analysis (GRA), an optimal factor setting which can take all qualities into account was found and had better deposition results compared with previous setting. Furthermore, ANOVAs were conducted to find out significant factors of each qualities. By using the significant factors as variations, three second-order polynomial regression predictive models for qualities were created. Based on the GRA and ANOVAs results, additional one-factor-at-a-time (OFAT) experiments which used the optimal setting as the center point were performed. The qualities variation resulting from adjusting overlap ratio and laser defocus distance of optimal setting were investigated, and the results were also used as additional data to verified the accuracies of three regression models.