Fig. 1

Schematic representation of methanol metabolism, 3-HP production via the β-alanine pathway, and carboxylic acids transport mechanisms reported in yeast. The pathway of 3-HP synthesis is shaded in green; and the methanol dissimilatory pathway is shaded in red. Heterologous enzymes are indicated with colored gears. While uncharged 3-HP (HOCH₂CH₂COOH) can passively diffuse across the plasma membrane, its anionic form (HOCH₂CH₂COO⁻) is hypothesized to require active transport via ABC transporters or permeases (i.e., Jen1 symporter). Dissociation of 3-HP in the cytosol releases protons (H⁺), which are mainly extruded by H⁺-ATPases, maintaining pH balance and electrochemical potential across the membrane (Z∆pH) [70]. FDH1, NAD-dependent formate dehydrogenase; PseFDH(V9), mutated NADP-dependent formate dehydrogenase; PYC2, pyruvate carboxylase isoform 2; AAT2, aspartate aminotransferase 2; SpeAspDH, NAD- or NADP-dependent aspartate dehydrogenase; PAND, aspartate-1-decarboxylase; BAPAT, β-alanine-pyruvate aminotransferase; YDFG, 3-hydroxypropionate dehydrogenase