The wild type red fluorescent protein eqFP578 (from sea anemone Entacmaea quadricolor, k ex 5 552 nm, k em 5 578 nm) and its bright far-red fluorescent variant Katushka (k ex 5 588 nm, k em 5 635 nm) are characterized by the pronounced pH dependence of their fluorescence. The crystal structures of eqFP578f (eqFP578 with two point mutations improving the protein folding) and Katushka have been determined at the resolution ranging from 1.15 to 1.85 Å at two pH values, corresponding to low and high level of fluorescence. The observed extinguishing of fluorescence upon reducing pH in eqFP578f and Katushka has been shown to be accompanied by the opposite trans-cis and cis-trans chromophore isomerization, respectively. Asn143, Ser158, His197 and Ser143, Leu174, and Arg197 have been shown to stabilize the respective trans and cis fluorescent states of the chromophores in eqFP578f and Katushka at higher pH. The cis state has been suggested as being primarily responsible for the observed far-red shift of the emission maximum of Katushka relative to that of eqFP578f.

The yellow fluorescent protein phiYFPv ( em max ' 537 nm) with improved folding has been developed from the spectrally identical wild-type phiYFP found in the marine jellyfish Phialidium. The latter fluorescent protein is one of only two known cases of naturally occurring proteins that exhibit emission spectra in the yellow-orange range (535-555 nm). Here, the crystal structure of phiYFPv has been determined at 2.05 Å resolution. The 'yellow' chromophore formed from the sequence triad Thr65-Tyr66-Gly67 adopts the bicyclic structure typical of fluorophores emitting in the green spectral range. It was demonstrated that perfect antiparallel -stacking of chromophore Tyr66 and the proximal Tyr203, as well as Val205, facing the chromophore phenolic ring are chiefly responsible for the observed yellow emission of phiYFPv at 537 nm. Structure-based site-directed mutagenesis has been used to identify the key functional residues in the chromophore environment. The obtained results have been utilized to improve the properties of phiYFPv and its homologous monomeric biomarker tagYFP.

No abstract

Conformational analysis of two pairs of synthetic cyclodipeptides formed by interaction of both side chain functional groups [Formula: see text] and of the main and side chains [Formula: see text] was achieved by the method of molecular mechanics. The energetically optimal conformational states of the molecules under study were determined. It was shown that the conformational motility of cyclic system of the compounds under study depends on the relative arrangement of the amide groups and the number of atoms in the cycle.

No abstract