你的心头也有星辰大海——带你领略呼吸的奥秘

The sea of stars in your heart——bring you a taste of the mystery of breathing

呼吸作用是最基本的生命活动之一.20世纪初,科学家们发现了一系列可以进行电子传递的铁硫中心、卟啉环等辅基,而后又逐步鉴定出这些辅基固定在一系列的蛋白质复合物中.最近,人们发现这些蛋白质复合物并不是相互独立存在的,而是倾向于结合在一起形成呼吸体.

Respiration is one of the most basic features of living organisms, and this normally neglected process is orchestrated by a rather complicated molecule system. Mitochondria are the major place for respiration in mammals, and its shape can vary with different cell conditions, which in turn can influence the efficiency of respiration. Within mitochondria, respiratory chain complexes responsible for respiration are located on the inner membrane that can form a special structure termed as cristae. The shape of cristae is variable in different species and cell conditions. Within these crista junctions, a series of scaffold proteins （MICOS） lash the base of cristae. The respiratory chain complexes are located on the relatively flat surface of cristae, while the ATP synthase dimers are located at the edge curve of cristae and aligned to form ribbons. This arrangement can greatly avoid proton leakage across the large cristae surface, and enables the sink formed by the ATP synthase dimers to harness proton gradient with highest efficiency. Despite early theories that respiratory chain complexes perform their function independently and randomly scattered on cristae, recent researches show strong evidence that these complexes tend to form higher level organizations called supercomplex or respirasome. Respiration process in molecular level means the consumption of high energy electron donors and oxygen to produce water and release energy in the meanwhile. Each respiratory chain complex harness part of the released energy to perform conformational change and three major complexes pump protons from mitochondrial matrix to intermembrane space, thus transforming chemical energy into electrochemical gradient, which is again harnessed by another protein complex （complex V, ATP synthase） to perform conformational change and produce ATP molecules. In fact, the existence of repirasome makes this process more delicate and efficient. Other than randomly drifting on the inner membrane, in the respirasome these individual respiratory complexes are arranged in a pattern where their reaction active sites are close to each other and their common substrates are compartmented within pools. In this way the efficiency of electron transfer can be greatly promoted, and the formation of supercomplex can stabilize the structure of individual complexes. Furthermore, in respirasome, the amount of reactive oxygen species generated during electron transfer is greatly reduced. Respiratory chaim malfunction can cause a series of serious diseases, including Alzheimer＇s and Parkinson＇s diseases, multiple sclerosis, Friedreich＇s ataxia, amyotrophic lateral sclerosis, Hurthle cell thyroid carcinoma （HCTC）, Leber＇s hereditary optic neuropathy （LHON）, lethal infantile mitochondrial disease （LIMD）, Leigh syndrome （LS）, linear skin defects with multiple congenital anomalies 3 （LSDMCA3）, mitochondrial encephalomyopathy with lactic acidosis and stroke-like episodes syndrome （MELAS）, mitochondrial complex I deficiency （MT-C1D）, and, non-insulin-dependent diabetes mellitus （NIDDM）. The structure of respirasome will certainly provide precious information for conquering these diseases.