RESUMO
Conjunctival amelanotic malignant melanoma is a rare form of melanoma, which lacks visible pigment and is commonly located underneath the eyelids in the bulbar conjunctiva. In this report, we described a case of a Caucasian women in her 70s who presented with unilateral irritation and tenderness following cataract surgery. On eversion of the eyelid, two elevated pink lesions were noted. Tumour - Node - Metastasis staging with the American Joint Committee on Cancer staging system eighth edition was T3C and required multiple excisions and reconstruction procedures. This case exemplified the diagnostic pitfall of conjunctival amelanotic malignant melanoma, which is a potentially life-threatening disease and the importance of histopathology in the diagnostic process.
Assuntos
Neoplasias da Túnica Conjuntiva , Melanoma Amelanótico , Neoplasias de Tecido Conjuntivo , Neoplasias Cutâneas , Humanos , Feminino , Melanoma Amelanótico/diagnóstico , Melanoma Amelanótico/cirurgia , Melanoma Amelanótico/patologia , Túnica Conjuntiva/patologia , Neoplasias da Túnica Conjuntiva/diagnóstico , Neoplasias da Túnica Conjuntiva/cirurgia , Neoplasias da Túnica Conjuntiva/patologia , Melanoma Maligno CutâneoRESUMO
Within the microbial rhodopsin family, heliorhodopsins (HeRs) form a phylogenetically distinct group of light-harvesting retinal proteins with largely unknown functions. We have determined the 1.97 Å resolution X-ray crystal structure of Thermoplasmatales archaeon SG8-52-1 heliorhodopsin (TaHeR) in the presence of NaCl under acidic conditions (pH 4.5), which complements the known 2.4 Å TaHeR structure acquired at pH 8.0. The low pH structure revealed that the hydrophilic Schiff base cavity (SBC) accommodates a chloride anion to stabilize the protonated retinal Schiff base when its primary counterion (Glu-108) is neutralized. Comparison of the two structures at different pH revealed conformational changes connecting the SBC and the extracellular loop linking helices A-B. We corroborated this intramolecular signaling transduction pathway with computational studies, which revealed allosteric network changes propagating from the perturbed SBC to the intracellular and extracellular space, suggesting TaHeR may function as a sensory rhodopsin. This intramolecular signaling mechanism may be conserved among HeRs, as similar changes were observed for HeR 48C12 between its pH 8.8 and pH 4.3 structures. We additionally performed DEER experiments, which suggests that TaHeR forms possible dimer-of-dimer associations which may be integral to its putative functionality as a light sensor in binding a transducer protein.