Microtubules bind glyceraldehyde 3-phosphate dehydrogenase and modulate its enzyme activity and quaternary structure

Glycolytic enzymes and assembly of microtubule networks

The ability of glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), aldolase, pyruvate kinase (PK), and lactate dehydrogenase muscle-type (LDH(M)), to generate interactive microtubule networks was investigated. Bundles have previously been defined as the parallel alignment of several microtubules and are one form of microtubule networks. Utilizing transmission electron microscopy, interactive networks of microtubules as well as bundles were readily observed in the presence of GAPDH, aldolase, or PK. These networks appear morphologically as cross-linked microtubules, oriented in many different ways. Light scattering indicated that the muscle forms of GAPDH, aldolase, PK and LDH(m) caused formation of the microtubule networks. Triose phosphate isomerase (TPI) and lactate dehydrogenase heart-type (LDH(H)), glycolytic enzymes which do not interact with tubulin or microtubules, did not produce bundles, or interactive networks. Sedimentation experiments confirmed that the enzymes that cross-link also co-pellet with the microtubules. Such cross-linking of microtubules indicate that the enzymes are multivalent with the capability of simultaneous binding to more than one microtubule.

A mutation in glyceraldehyde 3-phosphate dehydrogenase alters endocytosis in CHO cells

The CHO cell mutant FD 1.3.25 exhibits both increased accumulation and altered distribution of endocytosed fluid phase tracers. Neither the rate of tracer internalization nor the kinetics of recycling from early endosomes was affected, but exocytosis from late endocytic compartments appeared to be decreased in the mutant. Endocytosed tracer moved more rapidly to the cell poles in FD1.3.25 than in wild type cells. An abundant 36-kD polypeptide was found associated with taxol-polymerized microtubules in preparations from wild type and mutant; in the former but not the latter this polypeptide could be dissociated by incubation of the microtubules in ATP or high salt. The 36-kD polypeptide co-electrophoresed in two dimensions with the monomer of the glycolytic enzyme glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Analysis of cDNA clones showed that the mutant is heterozygous for this enzyme, with approximately 25% of the GAPDH RNA containing a single nucleotide change resulting in substitution of Ser for Pro234, a residue that is conserved throughout evolution. Stable transfectants of wild type cells expressing the mutant monomer at approximately 15% of the total enzyme exhibited the various changes in endocytosis observed in FD1.3.25.

Glycolytic enzyme-tubulin interactions: role of tubulin carboxy terminals

Tubulin and microtubules were modified with the protease, subtilisin. The modification reduced the length of alpha- or beta-tubulin by cleaving a peptide fragment from the C-terminals. Generation of alpha'beta'-tubulin, which is cleaved at both the alpha- and beta-subunit terminals, and alpha beta'-tubulin, which is cleaved at the beta-subunit C-terminal, have already been reported. In this work an isotype, alpha'beta-tubulin, was produced. The three modified tubulin isotypes were compared for their ability to interact with glycolytic enzymes. Cleavage of alpha led to a poorer interaction when tested via affinity chromatography. Tubulin also inhibits the activity of aldolase and glyceraldehyde 3-phosphate dehydrogenase. When the alpha-subunit C-terminal was intact, inhibition was greatest. These results imply that the C-terminal of the tubulin alpha-subunit is responsible for interactions with glycolytic enzymes.

Rat brain glyceraldehyde-3-phosphate dehydrogenase interacts with the recombinant cytoplasmic domain of Alzheimer's beta-amyloid precursor protein

Abundant senile plaques are a histological hallmark in the brain of Alzheimer's disease patients. Such plaques consist of, among many other constituents, aggregated beta A4 amyloid peptide. This peptide is derived from an amyloid precursor protein (APP) by irregular proteolytic processing and is considered to be involved in the development of Alzheimer's disease. To study possible interactions of brain proteins with beta A4 amyloid or other fragments of APP, beta A4 amyloid and beta A4 amyloid extended to the C-terminus of APP were recombinantly produced as fusion proteins termed "Amy" and "AmyC," respectively. Using Amy and AmyC affinity chromatography, a 35-kDa protein from rat brain was isolated that bound tightly to AmyC but not to Amy, thus indicating an interaction of the protein with the C-terminus of APP. This 35-kDa protein was identified as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Binding of GAPDH to AmyC but not to Amy was confirmed by gel filtration. Although AmyC slightly reduced the Vmax of GAPDH, the same reduction was observed in the presence of Amy. These findings suggest that the interaction of the cytoplasmic domain of APP with GAPDH is unlikely to influence directly the rate of glycolysis but may serve another function.

Selective inhibition of Plasmodium falciparum aldolase by a tubulin derived peptide and identification of the binding site

Aldolase of the human malaria parasite Plasmodium falciparum (PfAldo) may be a potential target for the development of novel antimalarial drugs. Using in vitro mutagenesis we analyzed the function of the carboxy-terminus of the recombinant enzyme. Deletion of the carboxy-terminus of PfAldo confirmed its critical role in catalysis; exchange of conserved residues minimally affected enzyme activity. We exchanged a pair of parasite specific lysine residues with corresponding amino acids of the host. These mutant enzymes exhibited an increased catalytic activity and reduced binding to erythrocyte band 3 protein. Homologous peptides of human band 3 protein and P. falciparum alpha-tubulin were competitive inhibitors of PfAldo. Selective inhibition of PfAldo by the alpha-tubulin peptide depends on the presence of tandem lysine residues and the fine structure of the inhibitor peptide. Our data support the concept of a matrix organisation of glycolytic enzymes in Plasmodium falciparum.

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH, E.C. 1.2.1.12.) gene expression in two malignant human mammary epithelial cell lines: BT-20 and MCF-7. Regulation of gene expression by 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3)

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a key enzyme in the control of glycolysis. Its gene expression was analyzed in two breast cancer cell lines of human origin, BT-20 and MCF-7. We used a cDNA probe of 1.3 kb for Northern blot hybridization. It is found that GAPDH mRNA is overexpressed only in the poorly differentiated BT-20 cell line and that treatment of these cells by 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) stimulates GAPDH mRNA expression in a dose-and time-dependent manner. The present investigation on the BT-20 cells indicates that the expression of GAPDH is sensitive to 1,25-(OH)2D3 and up-regulated by low doses of this steroid.

Association of glycolytic enzymes with the cytoskeleton

The diverse physical associations of the glycolytic enzymes with structural components of the cell suggest that the glycolytic enzymes are not entirely soluble in the cell. The relatively low affinities of the associations are likely responsible for the apparently transient interactions. The binding phenomenon is suggested to regulate metabolism through changes in enzymatic activity and facilitates localized enrichment of the enzymes.

Glyceraldehyde-3-phosphate dehydrogenase is a microtubule binding protein in a human colon tumor cell line

A protein which binds to tubulin polymer was isolated from a human colonic tumor cell line. This protein has a molecular mass of 35 kDa, as determined by polyacrylamide slab gel electrophoresis. The protein was purified by affinity chromatography on taxol-stabilized microtubules, and it did not cross-react with anti-MAP2 or anti-tau antibodies. This protein was identified as glyceraldehyde-3-phosphate dehydrogenase by its enzyme activity and immunoblotting experiments. The purified protein caused a pronounced enhancement in the turbidity increase produced by in vitro tubulin polymerization, and electron microscopic observations revealed the presence of bundles of microtubules.