A Novel Form of 6-Phosphofructokinase

Classically, 6-phosphofructokinases are homo- and hetero-oligomeric enzymes consisting of α subunits and α/β subunits, respectively. Herein, we describe a new form of 6-phosphofructokinase (Pfk) present in several Pichia species, which is composed of three different types of subunit, α, β, and γ. The sequence of the γ subunit shows no similarity to classic Pfk subunits or to other known protein sequences. In-depth structural and functional studies revealed that the γ subunit is a constitutive component of Pfk from Pichia pastoris (PpPfk). Analyses of the purified PpPfk suggest a heterododecameric assembly from the three different subunits. Accordingly, it is the largest and most complex Pfk identified yet. Although, the γ subunit is not required for enzymatic activity, the γ subunit-deficient mutant displays a decreased growth on nutrient limitation and reduced cell flocculation when compared with the P. pastoris wild-type strain. Subsequent characterization of purified Pfks from wild-type and γ subunit-deficient strains revealed that the allosteric regulation of the PpPfk by ATP, fructose 2,6-bisphosphate, and AMP is fine-tuned by the γ subunit. Therefore, we suggest that the γ subunit contributes to adaptation of P. pastoris to energy resources.