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Structural changes in bacteriorhodopsin during the photocycle measured by time-resolved polarized Fourier transform infrared spectroscopy.

ABSTRACT: The structural changes in bacteriorhodopsin during the photocycle are investigated. Time resolved polarized infrared spectroscopy in combination with photoselection is used to determine the orientation and motion of certain structural units of the molecule: Asp-85, Asp-96, Asp-115, the Schiff base, and several amide I vibrations. The results are compared with recently published x-ray diffraction data with atomic resolution about conformational motions during the photocycle. The orientation of the measured vibrations are also calculated from the structure data, and based on the comparison of the values from the two techniques new information is obtained: several amide I bands in the infrared spectrum are assigned, and we can also identify the position of the proton in the protonated Asp residues.

SUBMITTER: Kelemen L

PROVIDER: S-EPMC1301812 | biostudies-other | 2001 Dec

REPOSITORIES: biostudies-other

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Structural changes in bacteriorhodopsin during the photocycle measured by time-resolved polarized Fourier transform infrared spectroscopy.

Kelemen L L Ormos P P

Biophysical journal 20011201 6

The structural changes in bacteriorhodopsin during the photocycle are investigated. Time resolved polarized infrared spectroscopy in combination with photoselection is used to determine the orientation and motion of certain structural units of the molecule: Asp-85, Asp-96, Asp-115, the Schiff base, and several amide I vibrations. The results are compared with recently published x-ray diffraction data with atomic resolution about conformational motions during the photocycle. The orientation of th ...[more]

PMID: 11721018

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Project description:Fourier transform infrared (FTIR) spectroscopy, a technology traditionally used in chemistry to determine the molecular composition of a wide range of sample types, has gained growing interest in microbial typing. It is based on the different vibrational modes of the covalent bonds between atoms of a given sample, as bacterial cells, induced by the absorption of infrared radiation. This technique has been largely used for the study of pathogenic species, especially in the clinical field, and has been proposed also for the typing at different subspecies levels. The high throughput, speed, low cost, and simplicity make FTIR spectroscopy an attractive technique also for industrial applications, in particular, for probiotics. The aim of this study was to compare FTIR spectroscopy with established genotyping methods, pulsed-field gel electrophoresis (PFGE), whole-genome sequencing (WGS), and multilocus sequence typing (MLST), in order to highlight the FTIR spectroscopy potential discriminatory power at strain level. Our study focused on bifidobacteria, an important group of intestinal commensals generally recognized as probiotics. For their properties in promoting and maintaining health, bifidobacteria are largely marketed by the pharmaceutical, food, and dairy industries. Strains belonging to Bifidobacterium longum subsp. longum and Bifidobacterium animalis subsp. lactis were taken into consideration together with some additional type strains. For B. longum subsp. longum, it was possible to discriminate the strains with all the methods used. Although two isolates were shown to be strictly phylogenetically related, constituting a unique cluster, based on PFGE, WGS, and MLST, no clustering was observed with FTIR. For B. animalis subsp. lactis group, PFGE, WGS, and MLST were non-discriminatory, and only one strain was easily distinguished. On the other hand, FTIR discriminated all the isolates one by one, and no clustering was observed. According to these results, FTIR analysis is not only equivalent to PFGE, WGS, and MLST, but also for some strains, in particular, for B. animalis subsp. lactis group, more informative, being able to differentiate strains not discernible with the other two methods based on phenotypic variations likely deriving from certain genetic changes. Fourier transform infrared spectroscopy has highlighted the possibility of using the cell surface as a kind of barcode making tracing strains possible, representing an important aspect in probiotic applications. Furthermore, this work constitutes the first investigation on bifidobacterial strain typing using FTIR spectroscopy.

Project description:Probiotic bacteria, capable of conferring benefits to the host, can present challenges in design, development, scale-up, manufacturing, commercialization, and life cycle management. Strain identification is one of the main quality parameters; nevertheless, this task can be challenging since established methodologies can lack resolution at the strain level for some microorganisms and\or are labor-intensive and time-consuming. Fourier transform infrared spectroscopy (FTIRS) has been largely used for the investigation of pathogenic species in the clinical field, whereas only recently has been proposed for the identification of probiotic strains. Within the probiotic industrial production, bacterial strains can be subjected to stressful conditions that may affect genomic and phenotypic characteristics; therefore, real-time monitoring of all the sequential growth steps is requested. Considering the fast, low-cost, and high-throughput features, FTIRS is an innovative and functional technology for typing probiotic strains from bench-top experiments to large-scale industrial production, allowing the monitoring of stability and identity of probiotic strains. In this study, the discriminatory power of FTIRS was assessed for four Lactiplantibacillus plantarum probiotic strains grown under different conditions, including temperatures (30 and 37°C) and medium (broth and agar), after consecutive sub-culturing steps. A comparison between the generated spectra with pulsed-field gel electrophoresis (PFGE) profiles was also performed. FTIRS was not only able to distinguish the strains of L. plantarum under different growth conditions but also to prove the phenotypic stability of L. plantarum type strain LP-CT after six growing steps. Regardless of the growth conditions, FTIRS spectra related to LP-CT constituted a unique hierarchical cluster, separated from the other L. plantarum strains. These results were confirmed by a PFGE analysis. In addition, based on FTIRS data, broth cultures demonstrated a higher reproducibility and discriminatory power with respect to agar ones. These results support the introduction of FTIRS in the probiotic industry, allowing for the step-by-step monitoring of massive microbial production while also guaranteeing the stability and purity of the probiotic strain. The proposed novel approach can constitute an impressive improvement in the probiotic manufacturing process.

Dataset Information

Structural changes in bacteriorhodopsin during the photocycle measured by time-resolved polarized Fourier transform infrared spectroscopy.

Publications

Structural changes in bacteriorhodopsin during the photocycle measured by time-resolved polarized Fourier transform infrared spectroscopy.

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