Mutations in transhydrogenase change the fluorescence emission state of TRP72 from 1La to 1Lb

Spectra of tryptophan fluorescence are the result of co-existence of certain most abundant stabilized excited state and certain most abundant destabilized excited state

Fluorescence spectra of proteins and peptides are traditionally used to get an information on self-association of proteins and peptides, on their tertiary and quaternary structure. In this study it was shown that there are just three peaks of tryptophan fluorescence (at ∼308, at ∼330, and at ∼360 nm) in rough unsmoothed spectra of fluorescence of pure tryptophan in different solvents that change their heights depending on the polarity of a solvent. Two separate peaks at ∼330 nm and ∼360 nm are especially prominent in the spectrum of human epidermal growth factor. In contrast, in smoothed (either mathematically, or physically) spectra of Trp-containing proteins a single maximum of fluorescence varies between 330 and 360 nm. The theory of tryptophan fluorescence is discussed in light of three discrete peaks existence. A stabilizing hydrogen bond with aromatic system of benzene ring in the excited state is proposed as the cause of emission at ∼360 nm bringing Trp to the destabilized ground state. Emission from the destabilized excited state has a maximum at ∼330 nm if the ground state is destabilized, as well as if both states are stabilized. If the excited state is destabilized, while the ground state is stabilized by purely hydrophobic interactions, emitted light should have a maximum at ∼308 nm. The degree of hydrophilicity of tryptophan microenvironment is proposed to be measured as the ratio between the peak at 360 nm and the peak at 330 nm if the observed shifts are not "horizontal", but "vertical". The process of dissociation of hemagglutinin trimers from pandemic Influenza A(H1N1) virus is described as an example of the advantages of the proposed method.

MD + QM correlations with tryptophan fluorescence spectral shifts and lifetimes

Principles behind quenching of tryptophan (Trp) fluorescence are updated and extended in light of recent 100-ns and 1-μs molecular dynamics (MD) trajectories augmented with quantum mechanical (QM) calculations that consider electrostatic contributions to wavelength shifts and quenching. Four studies are summarized, including (1) new insight into the single exponential decay of NATA, (2) a study revealing how unsuspected rotamer transitions affect quenching of Trp when used as a probe of protein folding, (3) advances in understanding the origin of nonexponential decay from 100-ns simulations on 19 Trps in 16 proteins, and (4) the correlation of wavelength with lifetime for decay-associated spectra (DAS). Each study strongly reinforces the concept that-for Trp-electron transfer-based quenching is controlled much more by environment electrostatic factors affecting the charge transfer (CT) state energy than by distance dependence of electronic coupling. In each case, water plays a large role in unexpected ways.

Development of a fluorescence model for the binding of medium- to long-chain perfluoroalkyl acids to human serum albumin through a mechanistic evaluation of spectroscopic evidence

A novel model for measuring the strength of perfluoroalkyl acid (PFAA) binding to human serum albumin (HSA) by use of the protein's native fluorescence is described. The model is derived from published properties of HSA and its interactions with other surfactants; it is consistent with these properties and experimental observations. The model's validity has been tested with both medium- to long-chain PFAAs (perfluoroheptanoate, perfluorooctanoate, perfluorononanoate, perfluorodecanoate, perfluoroundecanoate, perfluorohexanesulfonate, and perfluorooctanesulfonate) and short-chain PFAAs (perfluorohexanoate and perfluorobutanesulfonate). These experiments confirm the model as a valid description for the binding of medium- to long-chain PFAAs to HSA. Results indicate at least 2-3 PFAAs bind to each protein with affinity on the order of 10(4) M(-1). These binding strengths exhibit a dependence on protein concentration. Measured PFAA binding constants are approximately 10% of those values reported for fatty acids of similar chain length; correcting for protein concentration suggests the binding strengths may be as low as 2-3% of the corresponding fatty acids' affinities. Like fatty acids, the carboxylate PFAAs exhibit a trend of generally increasing binding strength with increased chain length. The model does not appear valid for the binding of short-chain PFAAs to HSA. Hill binding coefficients, fluorescence intensity measurements, and wavelengths of maximum emission suggest short-chain PFAAs associate with HSA differently and fail to promote the same conformational changes in the protein's tertiary structure as the medium- to long-chain PFAAs.

The specificity of proton-translocating transhydrogenase for nicotinamide nucleotides

In its forward direction, transhydrogenase couples the reduction of NADP(+) by NADH to the outward translocation of protons across the membrane of bacteria and animal mitochondria. The enzyme has three components: dI and dIII protrude from the membrane and dII spans the membrane. Hydride transfer takes place between nucleotides bound to dI and dIII. Studies on the kinetics of a lag phase at the onset of a "cyclic reaction" catalysed by complexes of the dI and dIII components of transhydrogenase from Rhodospirillum rubrum, and on the kinetics of fluorescence changes associated with nucleotide binding, reveal two features. Firstly, the binding of NADP(+) and NADPH to dIII is extremely slow, and is probably limited by the conversion of the occluded to the open state of the complex. Secondly, dIII can also bind NAD(+) and NADH. Extrapolating to the intact enzyme this binding to the "wrong" site could lead to slip: proton translocation without change in the nucleotide redox state, which would have important consequences for bacterial and mitochondrial metabolism.