T-to-R switch of muscle fructose-1,6-bisphosphatase involves fundamental changes of secondary and quaternary structure

Abstract

When crystallized in the absence of the allosteric inhibitor AMP, human muscle fructose-1,6-bisphosphatase has a totally unexpected quaternary structure of its active R form, with the two dimers of the homotetrameric molecule in a perpendicular orientation, in stark contrast to the coplanar arrangement of the closely related liver isozyme. The T-to-R switch of the muscle enzyme also involves a highly unusual α→β refolding of the N-terminus.

Quadruple space-group ambiguity owing to rotational and translational noncrystallographic symmetry in human liver fructose-1,6-bisphosphatase

“…In human liver FBPases the average rotation angle of the T state is 14.5 AE 0.4 (n = 15, range 13.9-15.1 ), which is very similar to that observed in porcine FBPase T-state structures of 14.2 AE 1.2 (n = 30, range 10.5-17.1 ). Three hmFBPase structures have similar rotation angles of 15.6 AE 0.2 (range 15.4-15.7 ;Zarzycki et al, 2011;Barciszewski et al, 2016), which would indicate that the amount of rotation in FBPases is generally of the order of 15 . This view has been challenged by a recent hmFBPase structure that showed a cruciform arrangement of the dimers, i.e.…”

“…30 out of 90 structures in the PDB, including pig, rabbit and human FBPases, crystallized in five different space groups and contain only a single subunit in the asymmetric unit. The tetramer is constructed by crystallographic symmetry operations (Choe et al, 1998(Choe et al, , 2000Weeks et al, 1999;Choe, Iancu et al, 2003;Choe, Nelson et al, 2003;Iancu et al, 2005;Shi et al, 2013;Gao et al, 2013;Barciszewski et al, 2016). 50 more FBPase structures in three different space groups have a C1/C2 dimer in the asymmetric unit, and the tetramer is also completed by crystallographic symmetry.…”

“…This view has been challenged by a recent hmFBPase structure that showed a cruciform arrangement of the dimers, i.e. a rotation angle of close to 90 (Barciszewski et al, 2016). Since the human muscle and liver FBPase isoforms share only 76.9% sequence identity (89.3% homology) over 337 residues and the muscle isoform has additional functions in the cell, including higher sensitivity of hmFBPase to AMP and its regulation by Ca 2+ (Gizak et al, 2012;Pirog et al, 2014), some differences in their R/T transition behaviour might be expected.…”

“…Structural information on FBPases is available for porcine (no isoforms), rabbit, human liver and human muscle FBPases in the T state (Ke, Zhang et al, 1990;Gidh-Jain et al, 1994;Iversen et al, 1997;Barciszewski et al, 2016) and for porcine and human muscle FBPase in the R state (Ke et al, 1989;Ke, Zhang et al, 1990Choe et al, 1998Choe et al, , 2000Xue et al, 1994;Weeks et al, 1999;Barciszewski et al, 2016). Crystal structures of porcine FBPase in complex with various ligands established that the R and T states differ from each other by an $15 rotation of the dimers about the principal molecular axis (Ke, Zhang et al, 1990;Choe et al, 1998).…”

Structures of Leishmania Fructose-1,6-Bisphosphatase Reveal Species-Specific Differences in the Mechanism of Allosteric Inhibition

“…Mammalian FBPases (especially pig and human FBPases) are enzymologically and structurally well characterized [9] , [10] . The enzymes occur as very similar liver and muscle isoforms and are homotetramers assembled as a pair of dimers.…”