How the N-terminal Domain of the OSCP Subunit of Bovine F1Fo-ATP Synthase Interacts with the N-terminal Region of an Alpha Subunit

The peripheral stalk of ATP synthase acts as a stator holding the alpha(3)beta(3) catalytic subcomplex and the membrane subunit a against the torque of the rotating central stalk and attached c ring. In bovine mitochondria, the N-terminal domain of the oligomycin sensitivity conferral protein (OSCP-NT; residues 1-120) anchors one end of the peripheral stalk to the N-terminal tails of one or more alpha subunits of the F(1) subcomplex. Here, we present an NMR characterisation of the interaction between OSCP-NT and a peptide corresponding to residues 1-25 of the alpha-subunit of bovine F(1)-ATPase. The interaction site contains adjoining hydrophobic surfaces of helices 1 and 5 of OSCP-NT binding to hydrophobic side-chains of the alpha-peptide.

Structure of the F1-binding domain of the stator of bovine F1Fo-ATPase and how it binds an alpha-subunit

The peripheral stalk of ATP synthase holds the alpha3beta3 catalytic subcomplex stationary against the torque of the rotating central stalk. In bovine mitochondria, the N-terminal domain of the oligomycin sensitivity conferral protein (OSCP-NT; residues 1-120) anchors one end of the peripheral stalk to the N-terminal tails of one or more alpha-subunits of the F1 subcomplex. Here we present the solution structure of OSCP-NT and an NMR titration study of its interaction with peptides representing N-terminal tails of F1 alpha-subunits. The structure comprises a bundle of six alpha-helices, and its interaction site contains adjoining hydrophobic surfaces of helices 1 and 5; residues in the region 1-8 of the alpha-subunit are essential for the interaction. The OSCP-NT is similar to the N-terminal domain of the delta-subunit from Escherichia coli ATP synthase (delta-NT), except that their surface charges differ (basic and acidic, respectively). As the charges of the adjacent crown regions in their alpha3beta3 complexes are similar, the OSCP-NT and delta-NT probably do not contact the crowns extensively. The N-terminal tails of alpha-subunit tails are probably alpha-helical, and so this interface, which is essential for the rotary mechanism of the enzyme, appears to consist of helix-helix interactions.

Solution Structure of Subunit F6 from the Peripheral Stalk Region of ATP Synthase from Bovine Heart Mitochondria

The ATP synthase enzyme structure includes two stalk assemblies, the central stalk and the peripheral stalk. Catalysis involves rotation of the central stalk assembly together with the membrane-embedded ring of c-subunits driven by the trans-membrane proton-motive force, while the alpha and beta-subunits of F(1) are prevented from co-rotating by their attachment to the peripheral stalk. In the absence of structures of either the intact peripheral stalk or larger complexes containing it, we are studying its individual components and their interactions to build up an overall picture of its structure. Here, we describe an NMR structural characterisation of F(6), which is a 76-residue protein located in the peripheral stalk of the bovine ATP synthase and is essential for coupling between the proton-motive force and catalysis. Isolated F(6) has a highly flexible structure comprising two helices packed together through a loose hydrophobic core and connected by an unstructured linker. Analysis of chemical shifts, (15)N relaxation and RDC measurements confirm that the F(6) structure is flexible on a wide range of timescales ranging from nanoseconds to seconds. The relationship between this structure for isolated F(6) and its role in the intact peripheral stalk is discussed.

Homologous and heterologous inhibitory effects of ATPase inhibitor proteins on F-ATPases

In Saccharomyces cerevisiae, at least three proteins (IF(1), STF(1), and STF(2)) appear to be involved in the regulation of ATP synthase. Both IF(1) and STF(1) inhibit F(1), whereas the proposed function for STF(2) is to facilitate the binding of IF(1) and STF(1) to F(1). The oligomerization properties of yeast IF(1) and STF(1) have been investigated by sedimentation equilibrium analytical ultracentrifugation and by covalent cross-linking. Both techniques confirm that IF(1) and STF(1) oligomerize in opposite directions in relation to pH, suggesting that both proteins might regulate yeast F(1)F(0)-ATPase under different conditions. Their effects on bovine F-ATPases are also described. Whereas bovine IF(1) inhibits yeast F(1)-ATPase even better than yeast IF(1) or STF(1), the capability of yeast IF(1) to inhibit the bovine enzyme is very low and decreases with time. Such an effect is also observed in the study of the homologous inhibition of yeast F(1)-ATPase. Yeast inhibitors are not as effective as their bovine counterpart, and the complex seems to dissociate gradually.

Solution structure of a C-terminal coiled-coil domain from bovine IF(1): the inhibitor protein of F(1) ATPase

Bovine IF(1) is a basic, 84 amino acid residue protein that inhibits the hydrolytic action of the F(1)F(0) ATP synthase in mitochondria under anaerobic conditions. Its oligomerization state is dependent on pH. At a pH value below 6.5 it forms an active dimer. At higher pH values, two dimers associate to form an inactive tetramer. Here, we present the solution structure of a C-terminal fragment of IF(1) (44-84) containing all five of the histidine residues present in the sequence. Most unusually, the molecule forms an anti-parallel coiled-coil in which three of the five histidine residues occupy key positions at the dimer interface.

Solution studies of chymotrypsin inhibitor-2 glutamine insertion mutants show no interglutamine interactions

Mutants of chymotrypsin inhibitor protein 2 have previously been studied in which 4 or 10 glutamine residues were inserted into the inhibitory loop of the protein between residues 59 and 60, as potential models for the behaviour of glutamine tracts in proteins associated with polyglutamine-expansion neurodegenarative diseases. These mutants form very stable monomers, dimers and trimers. Although the cause of oligomerisation was found to be domain-swapping, it was thought that the glutamine insertions might nevertheless show evidence of weak interglutamine interactions in solution that could mimic those occurring in disease-associated proteins. In the present NMR study, we used steady-state (15)N[(1)H] NOE measurements and chemical shift comparisons to characterise the motional properties of the inserted glutamines in these CI2 mutants. We found the glutamines to be highly mobile, with no evidence of interactions amongst them in either monomers or dimers.

Detection of natural abundance nitrogen-15 through phosphorus-31 using pulsed field gradients

NMR characterization of natural abundance (15)N in phosphorus-nitrogen compounds can be performed through (31)P using inverse detection methods. When the (31)P-(15)N scalar coupling is small, its observation is greatly disturbed by the residual signal coming from the 99.6% abundant (14)N isotopomer that usually is not completely suppressed by the phase cycle of the sequence. The combined use of pulsed field gradients to suppress this residual signal and the enhanced sensitivity (31)P, (15)N[(1)H]-esHSQC experiment affords artifact-free spectra with good signal-to-noise ratio, which allows the accurate measurement of (15)N NMR parameters such as chemical shifts and coupling constants with the benefits of phosphorus detection.

Inversion of the anomeric configuration of the transferred sugar during inactivation of the macrolide antibiotic oleandomycin catalyzed by a macrolide glycosyltransferase

Macrolides are a group of antibiotics structurally characterized by a macrocyclic lactone to which one or several deoxy-sugar moieties are attached. The sugar moieties are transferred to the different aglycones by glycosyltransferases (GTF). The OleI GTF of an oleandomycin producer, Streptomyces antibioticus, catalyzes the inactivation of this macrolide by glycosylation. The product of this reaction was isolated and its structure elucidated. The donor substrate of the reaction was UDP-alpha-D-glucose, but the reaction product showed a beta-glycosidic linkage. The inversion of the anomeric configuration of the transferred sugar and other data about the kinetics of the reaction and primary structure analysis of several GTFs are compatible with a reaction mechanism involving a single nucleophilic substitution at the sugar anomeric carbon in the catalytic center of the enzyme.

Glycosylation of macrolide antibiotics. Purification and kinetic studies of a macrolide glycosyltransferase from Streptomyces antibioticus

The oleD gene has been identified in the oleandomycin producer Streptomyces antibioticus and it codes a macrolide glycosyltransferase that is able to transfer a glucose moiety from UDP-glucose (UDP-Glc) to many macrolides. The glycosyltransferase coded by the oleD gene has been purified 371-fold from a Streptomyces lividans clone expressing this protein. The reaction product was isolated, and its structure determined by NMR spectroscopy. The kinetic mechanism of the reaction was analyzed using the macrolide antibiotic lankamycin (LK) as substrate. The reaction operates via a compulsory order mechanism. This has been shown by steady-state kinetic studies and by isotopic exchange reactions at equilibrium. LK binds first to the enzyme, followed by UDP-glucose. A ternary complex is thus formed prior to transfer of glucose. UDP is then released, followed by the glycosylated lankamycin (GS-LK). A pH study of the reaction was performed to determine values for the molecular pK values, suggesting possible amino acid residues involved in the catalytic process.