Aldolase A

ALDOA is a homotetramer and one of the three aldolase isozymes (A, B, and C), encoded by three different genes. The ALDOA gene contains 8 exons and the 5' UTR IB. Though ALDOA localizes to the nucleus, it lacks any known nuclear localization signals (NLS). ==Mechanism==

In mammalian aldolase, the key catalytic amino acid residues involved in the reaction are lysine and tyrosine. The tyrosine acts as an efficient hydrogen acceptor while the lysine covalently binds and stabilizes the intermediates. Many bacteria use two magnesium ions in place of the lysine. The numbering of the carbon atoms indicates the fate of the carbons according to their position in fructose 6-phosphate. ==Function==

ALDOA is a key enzyme in the fourth step of glycolysis, as well as in the reverse pathway gluconeogenesis. It catalyzes the reversible conversion of fructose-1,6-bisphosphate to glyceraldehydes-3-phosphate and dihydroxyacetone phosphate by aldol cleavage of the C3–C4 bond. As a result, it is a crucial player in ATP biosynthesis. ALDOA also contributes to other "moonlighting" functions such as muscle maintenance, regulation of cell shape and motility, striated muscle contraction, actin cytoskeleton organization, and regulation of cell proliferation. ALDOA likely regulates actin cytoskeleton remodeling through interacting with cytohesin-2 (ARNO) and Arf6. ALDOA is ubiquitously expressed in most tissues, though it is predominantly expressed in developing embryo and adult muscle. In lymphocytes, ALDOA is the predominant aldolase isoform. Within the cell, ALDOA typically localizes to the cytoplasm, but it can localize to the nucleus during DNA synthesis of the cell cycle S phase. This nuclear localization is regulated by the protein kinases AKT and p38. It is suggested that the nucleus serves as a reservoir for ALDOA in low glucose conditions. ALDOA has also been found in mitochondria. ALDOA is regulated by the energy metabolism substrates glucose, lactate, and glutamine. In human mast cells (MCs), ALDOA has been observed to undergo post-translational regulation by protein tyrosine nitration, which may alter its relative affinity for FBP and/or IP3. This change then affects IP3 and PLC signaling cascades in IgE-dependent responses. ==Clinical significance==

Aldolase A (ALDOA) is highly expressed in multiple cancers, including lung squamous cell carcinoma (LSCC), renal cancer, and hepatocellular carcinoma. It is proposed that ALDOA overexpression enhances glycolysis in these tumor cells, promoting their growth. In LSCC, its upregulation correlates with metastasis and poor prognosis, while its downregulation reduces tumor cell motility and tumorigenesis. Thus, ALDOA could be a potential LSCC biomarker and therapeutic drug target. Aldolase A deficiency is a rare, autosomal recessive disorder that is linked to hemolysis and accompanied by weakness, muscle pain, and myopathy. ==Interactive pathway map==

Aldolase A has been shown to interact with: • PLD2, • actin, • phospholipase D2, • light chain 8 of dynein, • erythrocyte anion exchanger Band 3 protein, • ryanodine receptor, • Cytohesin-2, and • V-ATPase (vacuolar-type H+-ATPase). ==See also==