selenoproteines

Selenoproteins are proteins that contain the amino acid selenocysteine. Selenocysteine is the 21st amino acid found in nature and is structurally similar to cysteine, with a selenium atom replacing the sulfur atom. This unique atom allows selenoproteins to participate in a variety of biochemical reactions, particularly those involving redox processes. The incorporation of selenocysteine into proteins is a complex and highly regulated process that occurs during translation. It requires a specific UGA codon in the messenger RNA, which normally signals termination, to be interpreted as a selenocysteine insertion signal. This is facilitated by a specific transfer RNA (tRNA), a selenocysteine insertion sequence (SECIS) element in the mRNA, and several accessory proteins.

The functions of selenoproteins are diverse and crucial for many biological processes. They are involved in antioxidant defense, acting as enzymes that neutralize reactive oxygen species and protect cells from oxidative damage. Examples include glutathione peroxidases, which are critical for preventing cellular damage from peroxides. Selenoproteins also play roles in thyroid hormone metabolism, immune function, and DNA synthesis and repair. The human genome encodes for approximately 25 different selenoproteins, highlighting their importance in mammalian physiology. Deficiencies in selenium, the essential trace element required for selenocysteine synthesis, can lead to reduced activity of these proteins and have been linked to various health issues, including impaired immune function and increased susceptibility to oxidative stress-related diseases.