Nanoscopic surfactant behavior of the porin MspA in aqueous media

The mycobacterial porin MspA is one of the most stable channel proteins known to date. MspA forms vesicles at low concentrations in aqueous buffers. Evidence from dynamic light scattering, transmission electron microscopy and zeta-potential measurements by electrophoretic light scattering indicate that MspA behaves like a nanoscale surfactant. The extreme thermostability of MspA allows these investigations to be carried out at temperatures as high as 343 K, at which most other proteins would quickly denature. The principles of vesicle formation of MspA as a function of temperature and the underlying thermodynamic factors are discussed here. The results obtained provide crucial evidence in support of the hypothesis that, during vesicle formation, nanoscopic surfactant molecules, such as MspA, deviate from the principles underlined in classical surface chemistry

Hematoma espontâneo recorrente de mama: revisão da literatura e relato de caso

BACKGROUND: Breast hematomas are common after traumas, surgeries, or contusions. They are rarely spontaneous, but they can occur spontaneously in patients with hematologic disease or with coagulation disorders. MATERIAL AND METHODS: The authors report a clinical case of a 48-year-old female with a 27-year history of paroxysmal nocturnal hemoglobinuria who underwent mammography screening because of a painless palpable moveable node in the upper inner quadrant of the right breast. RESULTS: Mammography showed a partially defined heterogeneous node of 35 mm without microcalcifications in the upper inner quadrant of the right breast which, associated with the clinical features, seemed to be an hematoma. Further mammography and ultrasound after 45 days showed retrocession of the lesion, and another mammography obtained after 60 days was normal. Seventy-five days after the first episode, the patient complained of another node with a skin bruise in the upper outer quadrant of the same breast, which seemed to be a recurrent hematoma. Two months later the mammography obtained was normal. CONCLUSION: Breast hematoma must be thought of as a differential diagnosis for a breast node, regardless of previous trauma or hematologic disorders.OBJETIVO: Os hematomas de mama são comuns após traumatismo, cirurgias ou contusões. Raramente são espontâneos, podendo ocorrer em pacientes com doença hematológica ou outras doenças associadas a distúrbios da coagulação sangüínea. MATERIAL E MÉTODOS: Os autores relatam o caso de paciente feminina, 48 anos, com diagnóstico e acompanhamento de Hemoglobinúria paroxística noturna há 27 anos, submetida a mamografia por apresentar em consulta de rotina nódulo palpável em quadrante superior interno (QSI ) da mama direita, móvel e indolor. RESULTADOS: A mamografia evidenciou nódulo heterogêneo, de 35 mm, em QSI da mama direita, de contorno parcialmente delimitado, sem microcalcificações, que correlacionado com a história clínica, sugeria o diagnóstico de hematoma. O controle evolutivo com mamografia e ecografia, após 45 dias mostrou substancial regressão da lesão e novo exame após 60 dias foi normal. Decorridos 75 dias do primeiro episódio, a paciente apresentou outro nódulo, agora associado a hematoma cutâneo, em quadrante superior externo da mesma mama, interpretado como novo hematoma. O controle clínico após dois meses do segundo episódio foi normal. CONCLUSÕES: A hipótese de hematoma deve ser considerada no diagnóstico diferencial de nódulo mamário, com ou sem história de trauma ou doença sistêmica associada

Chlorophylls, ligands and assembly of light-harvesting complexes in chloroplasts

Chlorophyll (Chl) b serves an essential function in accumulation of light-harvesting complexes (LHCs) in plants. In this article, this role of Chl b is explored by considering the properties of Chls and the ligands with which they interact in the complexes. The overall properties of the Chls, not only their spectral features, are altered as consequences of chemical modifications on the periphery of the molecules. Important modifications are introduction of oxygen atoms at specific locations and reduction or desaturation of sidechains. These modifications influence formation of coordination bonds by which the central Mg atom, the Lewis acid, of Chl molecules interacts with amino acid sidechains, as the Lewis base, in proteins. Chl a is a versatile Lewis acid and interacts principally with imidazole groups but also with sidechain amides and water. The 7-formyl group on Chl b withdraws electron density toward the periphery of the molecule and consequently the positive Mg is less shielded by the molecular electron cloud than in Chl a. Chl b thus tends to form electrostatic bonds with Lewis bases with a fixed dipole, such as water and, in particular, peptide backbone carbonyl groups. The coordination bonds are enhanced by H-bonds between the protein and the 7-formyl group. These additional strong interactions with Chl b are necessary to achieve assembly of stable LHCs