The determination of the separation of tyrosine-99 and tyrosine-138 in calmodulin: radiationless energy transfer

The potential application of organoids in breast cancer research and treatment

Tumor heterogeneity is a major challenge for breast cancer researchers who have struggled to find effective treatments despite recent advances in oncology. Although the use of 2D cell culture methods in breast cancer research has been effective, it cannot model the heterogeneity of breast cancer as found within the body. The development of 3D culture of tumor cells and breast cancer organoids has provided a new approach in breast cancer research, allowing the identification of biomarkers, study of the interaction of tumor cells with the microenvironment, and for drug screening and discovery. In addition, the possibility of gene editing in organoids, especially using the CRISPR/Cas9 system, is convenient, and has allowed a more detailed study of tumor behavior in models closer to the physiological condition. The present review covers the application of organoids in breast cancer research. The recent use of gene-editing systems to provide insights into therapeutic approaches for breast cancer, is highlighted. The study of organoids and the possibility of gene manipulation may be a step towards the personalized treatment of breast cancer, which has so far remained unattainable due to the high heterogeneity of breast cancer.

Nitration of Tyrosine Channels Photoenergy through a Conical Intersection in Water

Nitration of tyrosine occurs under oxidative stress in vivo. The product, 3-nitrotyrosine (3NY), has a dramatically decreased quantum yield and can be used as a molecular ruler. In this study, femtosecond transient absorption spectroscopy and quantum calculations were implemented to elucidate the photoinduced relaxation processes of anionic 3NY in water. Upon 400 nm excitation into an excited electronic state with notable charge-transfer (CT) character, a barrierless nitro-twisting motion rapidly (<100 fs) guides the chromophore into an adjacent twisted intramolecular CT state, therein reaching a sloped S₁/S₀ conical intersection on the ∼100 fs time scale. Once in the hot ground state, excess energy is further released through vibrational cooling with biexponential time constants of ∼140 and 680 fs in water. Nitro back-twisting occurs on longer time scales (∼1.1 and 9 ps in water), returning the system to original ground state. Systematic evaluations of excited-state potential energies of anionic 3NY were performed by density functional theory (DFT) and time-dependent DFT calculations, showing that intersystem crossing (ISC) from the first singlet state (S₁) to the first or second triplet state (T₁ or T₂) is unlikely. Inclusion of an explicit water molecule in calculations leads to improved mapping of the excited-state energy ordering of the second singlet state (S₂) and T₂, further diminishing ISC probability from S₁ and favoring an ultrafast internal conversion to S₀. These results provide deep insights into the highly efficient nonradiative decay of anionic 3NY in aqueous solution, with nitro-site-specific information that can help infer the characterization and potential optogenetic control of 3NY in protein environment.

Dityrosine formation in calmodulin: conditions for intermolecular cross-linking

The pattern and extent of photoactivated dityrosine formation in bovine brain calmodulin are strongly affected by the presence of superoxide dismutase during UV irradiation. The addition of the enzyme to Ca(2+)-containing solutions of calmodulin results in an altered distribution of the dityrosine-containing photoproducts, from a predominance of cross-linked monomer to a mixture of products with inter- and intramolecular cross-linking. When Ca2+ is absent, significant dityrosine formation occurs only in the presence of superoxide dismutase. Fractionation of the latter reaction mixture yields a dimer of calmodulin, corresponding to a single component in sedimentation equilibrium, a smaller amount of a more highly polymerized material, and virtually no cross-linked monomer--as was found in the absence of the enzyme [Malencik, D.A., & Anderson, S.R. (1987) Biochemistry 26, 695]. Although it is homogeneous in terms of molecular weight, the purified dimer contains three electrophoretic components. Chemical characterization demonstrates intermolecular cross-linking of Tyr-99 to Tyr-138 and probably of Tyr-99 to Tyr-99. On the average, 85-90% of the dimeric calmodulin molecules bind two molecules of smooth muscle myosin light chain kinase. Catalytic activity determinations with this enzyme detect no difference between the dimer and the native protein. Fluorescence anisotropy measurements of Ca2+ binding give a Hill coefficient of < or = 0.73 and a free Ca2+ concentration of approximately 11 microM at 50% saturation. The average pKa of the dityrosine cross-link in the dimeric calmodulin is 8.5-8.6 (+/- Ca2+). Sedimentation velocity experiments show that the average Ca(2+)-liganded dimer has an elongated structure, with a relative frictional ratio approximately 30% greater than that of the native monomer. In terms of functional properties, the dimeric calmodulin preparation is more like the native protein than it is like the previously reported cross-linked monomer.

Sites of interaction of calmodulin with trifluoperazine and glucagon

The combination of glucagon with calmodulin alters the microenvironment of Tyr-99, but not Tyr-138, and is blocked by the binding of trifluoperazine by calmodulin. Trp-25 of glucagon is probably involved in the zone of interaction, which may also overlap one or more strong binding sites for trifluoperazine. From energy transfer measurements, one strong binding site for trifluoperazine probably involves the N-terminal region of binding domain III. Energy transfer and other evidence suggest that the zone of contact with glucagon involves the N-terminal region of binding domain III.