Human Glyceraldehyde 3‐Phosphate Dehydrogenase‐2 Gene Is Expressed Specifically in Spermatogenic Cells

Abstract

Although the process of glycolysis is highly conserved in eukaryotes, several glycolytic enzymes have unique structural or functional features in spermatogenic cells. We previously identified and characterized the mouse complementary DNA (cDNA) and a gene for 1 of these enzymes, glyceraldehyde 3‐phosphate dehydrogenase‐s (Gapds). This gene is expressed only in spermatids. The enzyme appears to have an essential role in energy production required for fertilization, and it is reported to be susceptible to inhibition by certain environmental chemicals. We have now cloned and sequenced the cDNA for the human homo‐logue of glyceraldehyde 3‐phosphate dehydrogenase (GAPD2) and determined the structure of the gene. The messenger RNA (mRNA) was detected in testis, but not in 15 other human tissues analyzed by Northern blot technique. The deduced GAPD2 protein contains 408 amino acids and is 68% identical with somatic cell GAPD. GAPD2 has a 72‐amino acid segment at the amino terminal end that is not present in somatic cell GAPD. This segment is prolinerich but contains smaller stretches of polyproline and is 30 amino acids shorter than the comparable segment of mouse GAPDS. The structure of the human GAPD2 gene was determined by polymerase chain reaction (PCR) to identify exonintron junctions in a genomic clone and in total genomic DNA. The locations of these junctions in the GAPD2 gene corresponded precisely to those of the 11 exonintron junctions in the mouse Gapds gene. Immunohistochemical studies found that GAPD2 is located in the principal piece of the flagellum of human spermatozoa, as are GAPDS in mouse and rat spermatozoa. GAPD2 extracted from human spermatozoa and analyzed by Western blot technique migrated with an apparent molecular weight of ∼56 000, although the calculated molecular weight is 44501. The conserved nature of the mouse, rat, and human enzymes suggests that they serve similar roles in these and other mammalian species.

Energy metabolism in mammalian sperm motility

“…(b,c) Detailed metabolic pathways active in sperm. These rely on the function of several testis‐specific proteins and proteins derived from alternative transcripts, uniquely expressed in post‐meiotic germ cells (green): spermatogenic cell‐specific hexokinase 1 isozyme (HK1; Mori et al, 1998; Mori et al, 1996); glucose‐6‐phosphate isomerase (GPI; Buehr & McLaren, 1981); spermatogenic cell‐specific ATP‐dependent 6‐phosphofructokinase (PFKM; Nakamura et al, 2010); fructose‐biphosphate aldolases A (ALDOART1, ALDOART2, ALDOA_V2; Gillis & Tamblyn, 1984; Vemuganti et al, 2007); triosephosphate isomerase (TPI1; Ijiri et al, 2013; Russell & Kim, 1996); glyceraldehyde 3‐phosphate dehydrogenase, testis specific (GAPDHS; Welch et al, 2000; Welch et al, 1992); phosphoglycerate kinase 2 (PGK2; Boer et al, 1987; McCarrey & Thomas, 1987); phosphoglycerate mutase 2 (PGAM2; Broceno et al, 1995; Fundele et al, 1987); enolase 4 (ENO4; Edwards & Grootegoed, 1983; Nakamura et al, 2013), pyruvate kinase PKM (PKM; Feiden et al, 2007); l ‐lactate dehydrogenase C chain (LDHC; Blanco & Zinkham, 1963; Millan et al, 1987); cytochrome c, testis‐specific (CYCT; Goldberg et al, 1977; Hennig, 1975); cytochrome c oxidase subunit 6B2 (COX6B2; Cheng et al, 2020; Huttemann et al, 2003); mitochondrial pyruvate carrier 1‐like protein (MPC1L; Vanderperre et al, 2016); pyruvate dehydrogenase E1 component subunit alpha, testis specific form, mitochondrial (PDHA2; Dahl et al, 1990; Korotchkina et al, 2006); succinyl‐CoA:3‐ketoacid coenzyme A transferase 2, mitochondrial (OXCT2; Koga et al, 2000; Tanaka et al, 2002); solute carrier family 22 member 14 (SLC22A14). (b) Sperm glycolytic pathway .…”

Three male germline-specific aldolase A isozymes are generated by alternative splicing and retrotransposition

“…We found that GAPDHS, aldolase A (ALDOA), lactate dehydrogenase A (LDHA), and pyruvate kinase remain attached to the fibrous sheath throughout a rigorous isolation procedure (Bunch et al, 1998;Krisfalusi et al, 2006). GAPDHS is larger than other GAPDH family members and contains a novel proline-rich extension at the N-terminus (Welch et al, 1992(Welch et al, , 2000 that may mediate binding to the fibrous sheath. Our proteomic and immunoblot analyses identified two ALDOA bands in mouse sperm, with the larger 50,000 molecular weight band always present in isolated fibrous sheaths (Krisfalusi et al, 2006).…”

A proteomic approach to identifying spermatozoa proteins in Indonesian native Madura bulls

“…Glycolysis is a significant mechanism for facilitating the transport of ATP along the flagellum. Westhoff and Kamp ( 44 ), as well as Welch et al ( 45 ), have reported the presence of glyceraldehyde 3-phosphate dehydrogenase (GAPDH) in significant quantities within the fibrous sheath of sperm from different mammalian species, including humans. GAPDH is a NAD-dependent glycolytic enzyme responsible for facilitating the conversion of glyceraldehyde 3-phosphate (GAP) to 1,3-biphosphoglycerate (1,3 BPG).…”