Sandbox GGC11

Alpha A and Alpha B Crystallins are a major protein component of the mammalian eye lens. Alpha crystallin is mainly found on the lens of the eye with trace amounts in other tissues while Alpha B is essentially considered a ubiquitous protein. ^[1]

Function

This protein contributes to the transparency and refractive index of the eye lens. Alpha- Crystallin can act as chaperones preventing the aggregation of various proteins.

Disease

Cataracts 9, multiple types

This disease is caused by mutations affecting the eye lens. This is an opacification of the crystalline sense of the eye, in most instances, may lead to impairment or blindness.

Myopathy, Miofibrillar

A group of chronic neuromuscular disorder characterized by the disintegration of the sarcomere Z disc and myofibrils. Myopathy is characterized by weakness of proximal and distal limbs, weakness of neck, hypertrophy cardiomyopathy, and cataracts in a subset of patients.

Myopathy, myofibrillar, fatal infantile hypertonic, alpha-B crystallin

This is another form of myopathy myofibril, but it happens in infants. It is a chronic neuromuscular disorder characterized by disintegration of sarcomere Z disc and myofibrils. MFMFIH-CRYAB has onset on the first weeks of life after the neonatal period. Affected infants show rapid muscular rigidity of trunks and limbs which is associated with increasing respiratory difficulties resulting in death before the age of 3.

Relevance

Alpha Crystallin A 1-172 is found at nearly 2 folds higher in diabetic lenses than an aged matched control lens. In humans, the alpha A gene is found in chromosome 21 and encodes for 173 amino acid residues while the alpha B gene is found in chromosome 11 and encodes for 175 amino acids.^[1] In mammalian lens, the molar ratio between alpha A and alpha B is a 3 to 1 ratio. ^[2]

Structural highlights

This structure highlight shows where is located in the A chain. A mutation of this amino acid to cysteine will lead to cataracts. ^[1]

The following structure shows where is located. The mutation of this amino acid in the B chain of crystalline gene decreased interaction with wild-type CRYAA and CRYAB. However, it increases interactions with CRBB2 and CRYGC leading to cytoplasmic aggregation. ^[3]

This highlight shows the location of the involved in inter-subunit bridging of Zn ions which enhances stability.^[4] This is crucial as there is no protein turnover in the lens.

The following structure shows with all the chains that make it up.

This sample structure shows the amino acid . When Arg is mutated to Gly, it causes desmin related myopathy, cardiomyopathy, and cataracts. Also, this mutation reduces chaperone protection activity and in some target proteins promoted aggregation. ^[1]