Probing nonenzymatic glycation of proteins by deep ultraviolet light emitting diode induced autofluorescence.

The suitability of deep-UV-LED (285 nm) as an excitation source to induce autofluorescence in nonenzymatically glycated proteins has been reported for the first time in this study. Non-enzymatically glycated proteins show high autofluorescence when excited with deep-UV light, i.e., deep-UV-induced autofluorescence (deep-UV-IAF). Multiple autofluorescence peaks of nonenzymatically glycated proteins between 300 and 600 nm when excited using the deep-UV-LED revealed structural and biochemical modifications. The partial unfolding of proteins in which Tryptophan (Trp) is either absent (e.g., RibonucleaseA) or the emission maxima of Trp is insensitive to nonenzymatic glycation (e.g., Human Serum Albumin and Bovine Serum Albumin) were elucidated using their Tyrosine (Tyr) emission (λem = ~320 nm). Also, the deep-UV-LED-induced autofluorescence (deep-UV-LED-IAF) is shown to detect and track a wide range of clinically relevant advanced glycation end-products (AGEs) such as Pentosidine (λem = ~380 nm), Argpyrimidine (λem = ~395 nm), Vesperlysine C (λem = ~405 nm), Vesperlysine A/B (λem = ~440 nm), Crossline (λem = ~480 nm), and Arginine derived AGEs (λem = ~525 nm) which is also supported by the chemometric analysis (PCA). The relevance of Trp/Tyr makeup of proteins in tracking AGEs using deep-UV-IAF has been carefully examined with proteins such as RibonucleaseA (RNaseA:zero Trp and six Tyr), Human Serum Albumin (HSA: one Trp and eighteen Tyr), Bovine Serum Albumin (BSA: two Trp and twenty Tyr) and Hemoglobin (Hb: four Trp and twelve Tyr). The Molecular Dynamic (MD) simulation revealed a high root-mean-square deviation (RMSD: 4.6 Å) and an increased average distance between Tyr residues and Trp214 (23.2 Å) in methylglyoxal (MG) treated HSA. This confirms the MG-induced protein unfolding and decreased fluorescence resonance energy transfer (FRET) from Tyr to Trp (Tyr â†’ Trp). The study also used systematic steady-state and time-resolved fluorescence (TRF) to explain the sudden decrease in AGEs specific fluorescence intensity and lifetime at higher concentrations of MG due to inter-AGEs FRET.

Interrogation of an autofluorescence-based method for protein fingerprinting.

In the present study, we have designed a laser-induced fluorescence (LIF) based instrumentation and developed a sensitive methodology for the effective separation, visualization, identification and analysis of proteins on a single platform. In this method, intrinsic fluorescence spectra of proteins were detected after separation on 1 or 2 dimensional Sodium Dodecyl Sulfate-Tris(2-carboxyethyl)phosphine (SDS-TCEP) polyacrylamide gel electrophoresis (PAGE) and the data were analyzed. The MATLAB assisted software was designed for the development of PAGE fingerprint for the visualization of protein after 1- and 2-dimensional protein separation. These provided objective parameters of intrinsic fluorescence intensity, emission peak, molecular weight and isoelectric point using a single platform. Further, the current architecture could differentiate the overlapping proteins in the PAGE gels which otherwise were not identifiable by conventional staining, imaging and tagging methods. Categorization of the proteins based on the presence or absence of tyrosine or tryptophan residues and assigning the corresponding emission peaks (309-356 nm) with pseudo colors allowed the detection of proportion of proteins within the given spectrum. The present methodology doesn't use stains or tags, hence amenable to couple with mass spectroscopic measurements. This technique may have relevance in the field of proteomics that is used for innumerable applications.

Identification of protein secondary structures by laser induced autofluorescence: A study of urea and GnHCl induced protein denaturation.

In the present study an attempt has been made to interrogate the bulk secondary structures of some selected proteins (BSA, HSA, lysozyme, trypsin and ribonuclease A) under urea and GnHCl denaturation using laser induced autofluorescence. The proteins were treated with different concentrations of urea (3M, 6M, 9M) and GnHCl (2M, 4M, 6M) and the corresponding steady state autofluorescence spectra were recorded at 281nm pulsed laser excitations. The recorded fluorescence spectra of proteins were then interpreted based on the existing PDB structures of the proteins and the Trp solvent accessibility (calculated using "Scratch protein predictor" at 30% threshold). Further, the influence of rigidity and conformation of the indole ring (caused by protein secondary structures) on the intrinsic fluorescence properties of proteins were also evaluated using fluorescence of ANS-HSA complexes, CD spectroscopy as well as with trypsin digestion experiments. The outcomes obtained clearly demonstrated GnHCl preferably disrupt helix as compared to the beta ß-sheets whereas, urea found was more effective in disrupting ß-sheets as compared to the helices. The other way round the proteins which have shown detectable change in the intrinsic fluorescence at lower concentrations of GnHCl were rich in helices whereas, the proteins which showed detectable change in the intrinsic fluorescence at lower concentrations of urea were rich in ß-sheets. Since high salt concentrations like GnHCl and urea interfere in the secondary structure analysis by circular dichroism Spectrometry, the present method of analyzing secondary structures using laser induced autofluorescence will be highly advantageous over existing tools for the same.