Glycine cleavage system H protein, mitochondrial (abbreviated as GCSH) is a protein that in humans is encoded by the GCSHgene.[4][5][6] Degradation of glycine is brought about by the glycine cleavage system (GCS), which is composed of 4 protein components: P protein (a pyridoxal phosphate-dependent glycine decarboxylase), H protein (a lipoic acid-containing protein; this protein), T protein (a tetrahydrofolate-requiring aminomethyltransferase enzyme), and L protein (a lipoamide dehydrogenase).[6] The H protein shuttles the methylamine group of glycine from the P protein to the T protein. The protein encoded by GCSH gene is the H protein, which transfers the methylamine group of glycine from the P protein to the T protein.[7] Defects in this gene are a cause of nonketotic hyperglycinemia (NKH).[8] Two transcript variants, one protein-coding and the other probably not protein-coding,have been found for this gene. Also, several transcribed and non-transcribed pseudogenes of this gene exist throughout the genome.[9]
Human GCSH gene has 5 exons spanning 13.5kb and resides on chromosome 16 at q23.2.[7]
Protein
The GCSH is a heat-stable small protein with a covalently attached lipoic acid prosthetic group which interacts with the three enzymes during the catalysis. The chemically determined amino acid sequence revealed that chicken H-protein is composed of 125 amino acids with a lipoic acid prosthetic group at lysine 59 (Lys59).[5] Because of its restricted tissue expression in humans, H-protein purified from chicken liver has been routinely used for the assay.[12] The H-protein comprises a mitochondrial targeting sequence and a mature mitochondrial matrix protein sequence. Its activation in vivo requires the attachment of a lipoic acid prosthetic group at Lys59 of the mature protein.[7] The matrix protein sequence is highly conserved and chicken H-protein has 85.6% amino acid sequence similarity to the human form.[13]
Clinical significance
Nonketotic hyperglycinemia (NKH) is an inborn error of metabolism caused by deficiency in the glycine cleavage system (GCS).[14] Enzymatic analysis has identified three metabolic lesions in NKH, deficiencies of P-, T-, and H-proteins.[9] The first mutation identified in NKH was in the P-protein gene.[15] Subsequently, some patients were found to have mutations in the T-protein gene.[16] The structure, polymorphism, and expression of GCSH could facilitate the molecular analysis of patients with variant forms of NKH that are caused by H-protein deficiency.[7]
^ abFujiwara K, Okamura-Ikeda K, Hayasaka K, Motokawa Y (Apr 1991). "The primary structure of human H-protein of the glycine cleavage system deduced by cDNA cloning". Biochemical and Biophysical Research Communications. 176 (2): 711–6. doi:10.1016/S0006-291X(05)80242-6. PMID2025283.
^Kikuchi G (Jun 1973). "The glycine cleavage system: composition, reaction mechanism, and physiological significance". Molecular and Cellular Biochemistry. 1 (2): 169–87. doi:10.1007/bf01659328. PMID4585091.
^ abcZay A, Choy FY, Patrick C, Sinclair G (Jun 2011). "Glycine cleavage enzyme complex: molecular cloning and expression of the H-protein cDNA from cultured human skin fibroblasts". Biochemistry and Cell Biology. 89 (3): 299–307. doi:10.1139/o10-156. PMID21539457.
^Hiraga K, Kure S, Yamamoto M, Ishiguro Y, Suzuki T (Mar 1988). "Cloning of cDNA encoding human H-protein, a constituent of the glycine cleavage system". Biochemical and Biophysical Research Communications. 151 (2): 758–62. doi:10.1016/s0006-291x(88)80345-0. PMID3348809.
^Fujiwara K, Okamura-Ikeda K, Motokawa Y (Jul 1986). "Chicken liver H-protein, a component of the glycine cleavage system. Amino acid sequence and identification of the N epsilon-lipoyllysine residue". The Journal of Biological Chemistry. 261 (19): 8836–41. PMID3522581.
^Choy F, Sharp L, Applegarth DA (2000). "Glycine cleavage enzyme complex: rabbit H-protein cDNA sequence analysis and comparison to human, cow, and chicken". Biochemistry and Cell Biology. 78 (6): 725–30. doi:10.1139/bcb-78-6-725. PMID11206584.
^Kure S, Narisawa K, Tada K (Feb 1991). "Structural and expression analyses of normal and mutant mRNA encoding glycine decarboxylase: three-base deletion in mRNA causes nonketotic hyperglycinemia". Biochemical and Biophysical Research Communications. 174 (3): 1176–82. doi:10.1016/0006-291x(91)91545-n. PMID1996985.
^Kure S, Mandel H, Rolland MO, Sakata Y, Shinka T, Drugan A, Boneh A, Tada K, Matsubara Y, Narisawa K (Apr 1998). "A missense mutation (His42Arg) in the T-protein gene from a large Israeli-Arab kindred with nonketotic hyperglycinemia". Human Genetics. 102 (4): 430–4. doi:10.1007/s004390050716. PMID9600239.
Further reading
Hiraga K, Kure S, Yamamoto M, Ishiguro Y, Suzuki T (Mar 1988). "Cloning of cDNA encoding human H-protein, a constituent of the glycine cleavage system". Biochemical and Biophysical Research Communications. 151 (2): 758–62. doi:10.1016/S0006-291X(88)80345-0. PMID3348809.
Gründig E, Birnbaumer E, Hawrylewicz A (1981). "Influence of phenothiazines or reserpine on the formation of 14C-glycine from U-14C-serine". Enzyme. 26 (1): 43–8. PMID6111451.
Kure S, Kojima K, Ichinohe A, Maeda T, Kalmanchey R, Fekete G, Berg SZ, Filiano J, Aoki Y, Suzuki Y, Izumi T, Matsubara Y (Nov 2002). "Heterozygous GLDC and GCSH gene mutations in transient neonatal hyperglycinemia". Annals of Neurology. 52 (5): 643–6. doi:10.1002/ana.10367. PMID12402263.
Rual JF, Venkatesan K, Hao T, Hirozane-Kishikawa T, Dricot A, Li N, Berriz GF, Gibbons FD, Dreze M, Ayivi-Guedehoussou N, Klitgord N, Simon C, Boxem M, Milstein S, Rosenberg J, Goldberg DS, Zhang LV, Wong SL, Franklin G, Li S, Albala JS, Lim J, Fraughton C, Llamosas E, Cevik S, Bex C, Lamesch P, Sikorski RS, Vandenhaute J, Zoghbi HY, Smolyar A, Bosak S, Sequerra R, Doucette-Stamm L, Cusick ME, Hill DE, Roth FP, Vidal M (Oct 2005). "Towards a proteome-scale map of the human protein-protein interaction network". Nature. 437 (7062): 1173–8. doi:10.1038/nature04209. PMID16189514.
