Selective Reactivity of H2S with GlnE7 and HisE7 in Hemoglobins: Implications for Organisms

生活在硫化物丰富的环境中的生物体中含有共生的化学自养细菌，这些细菌在氧气存在的情况下氧化硫化物并固定二氧化碳。负责向这些细菌输送硫化氢(H2S)和氧气的生物分子是血红素蛋白(Hb)。HB保护这些生物免受硫化氢毒害，并帮助维持它们与内共生菌物种的共生关系。这些无脊椎动物的血红蛋白在远端的化学结构和立体化学上表现出多样性。胞内血红蛋白通过血红素活性部位结合和运输其各自的配体，而胞外血红蛋白同时输送H_2S和O_2，利用血红素生色团外的巯基或有机金属锌簇输送H_2S。假设单一氨基酸(E7位的谷氨酰胺或组氨酸)是导致硫化氢毒性和血红素反应活性差异的原因。该项目的结果将使人们更深入地了解硫化氢运输的独特途径，以及降低硫化氢在特定生物体中的毒性。更广泛的影响这一跨学科研究项目将被用作教学工具，指导研究生和本科生，并通过访问当地学校向预科学生和教师进行科学演示，增加他们的知识和沟通技能。

Organisms that live in sulfide-rich environments harbor symbiotic chemoautotrophic bacteria that, in the presence of oxygen, oxidize sulfide and fix carbon dioxide. The biological molecule responsible for delivering hydrogen sulfide (H2S) and oxygen to these bacteria is the heme protein hemoglobin (Hb). Hb protects these organisms from H2S toxicity and helps maintain their symbiotic relationship with the endosymbiont species. Hemoglobins from these invertebrate organisms show variability in the distal chemical structure and stereochemistry. While cytoplasmic hemoglobins bind and transport their respective ligands via the heme active site, extracellular hemoglobins deliver H2S and O2 simultaneously, delivering H2S using sulfhydryl or organometallic Zn clusters outside the heme chromophore. It is hypothesized that a single amino acid (glutamine or histidine at position E7) is responsible for the difference in H2S toxicity and heme reactivity. The results of this project would provide a deeper understanding of the unique routes for hydrogen sulfide transport and the decreased hydrogen sulfide toxicity in particular organisms. BROADER IMPACTS This interdisciplinary research project will be used as teaching tool to mentor graduate and undergraduate students, as well as to increase their knowledge and communication skills through scientific presentations to pre-college students and teachers via visits to local schools.