Hedgehog (Hh) proteins function in cell/cell signaling processes linked to human embryo development and the progression of several types of cancer. Here we describe an optical assay of hedgehog cholesterolysis, a unique autoprocessing event critical for Hh function. The assay uses a recombinant FRET-active hedgehog precursor whose cholesterolysis can be monitored continuously in multi-well plates (dynamic range, 4; Z’, 0.7), offering advantages in throughput over conventional SDS-PAGE assays. Application of the optical assay in a pilot small molecule screen produced a novel cholesterolysis inhibitor (apparent IC50, 5×10−6 M) that appears to inactivate hedgehog covalently by a SNAr mechanism.

Hedgehog (Hh) signaling is driven by the cholesterol-modified Hh ligand, generated by autoprocessing of Hh precursor protein. Two steps in Hh autoprocessing, N–S acyl shift and transesterification, must be coupled for efficient Hh cholesteroylation and downstream signal transduction. In the present study, we show that a conserved aspartate residue, D46 of the Hh autoprocessing domain, coordinates these two catalytic steps. Mutagenesis demonstrated that D46 suppresses non-native Hh precursor autoprocessing and is indispensable for transesterification with cholesterol. NMR measurements indicated that D46 has a pKa of 5.6, ~2 units above the expected pKa of aspartate, due to a hydrogen-bond between protonated D46 and a catalytic cysteine residue. However, the deprotonated form of D46 side chain is also essential, because a D46N mutation cannot mediate cholesteroylation. On the basis of these data, we propose that the proton shuttling of D46 side chain mechanistically couples the two steps of Hh cholesteroylation.

Hedgehog proteins, signaling molecules implicated in human embryo development and cancer, can be inhibited at the stage of autoprocessing by the trivalent arsenical phenyl arsine oxide (PhAsIII). The interaction (apparent Ki, 4×10−7M) is characterized by an optical binding assay and by NMR spectroscopy. PhAsIII appears to be the first validated inhibitor of hedgehog autoprocessing, which is unique to hedgehog proteins and essential for biological activity.

Hedgehog (Hh) precursor proteins contain an autoprocessing domain called HhC whose native function is protein cleavage and C-terminal glycine sterylation. The transformation catalyzed by HhC occurs in cis from a precursor protein and exhibits wide tolerance toward both sterol and protein substrates. Here, we repurpose HhC as a 1:1 protein−nucleic acid ligase, with the sterol serving as a molecular linker. A procedure is described for preparing HhCactive sterylated DNA, called steramers, using aqueous compatible chemistry and commercial reagents. Steramers have K M values of 7−11 μM and reaction t 1/2 values of ∼10 min. Modularity of the HhC/steramer method is demonstrated using four different proteins along with structured and unstructured sterylated nucleic acids. The resulting protein−DNA conjugates retain the native solution properties and biochemical function. Unlike self-tagging domains, HhC does not remain fused to the conjugate; rather, enzymatic activity is mechanistically coupled to conjugate release. That unique feature of HhC, coupled with efficient kinetics and substrate tolerance, may ease access and open new applications for these suprabiological chimeras.

Background: In many types of cancers zinc deficiency and overproduction of Hedgehog (Hh) ligand co-exist. Results: Zinc binds to the active site of the Hedgehog-intein (Hint) domain and inhibits Hh ligand production both in vitro and in cell culture. Conclusion: Zinc influences the Hh autoprocessing.Significance: This study uncovers a novel mechanistic link between zinc and the Hh signaling pathway.

Three types of cone cells exist in the human retina, each containing a different pigment responsible for the initial step of phototransduction. These pigments are distinguished by their specific absorbance maxima: 425 nm (blue), 530 nm (green), and 560 nm (red). Each pigment contains a common chromophore, 11-cis-retinal covalently bound to an opsin protein via a Schiff base. The 11-cis-retinal protonated Schiff base has an absorbance maxima at 440 nm in methanol. Unfortunately, the chemistry that allows the same chromophore to interact with different opsin proteins to tune the absorbance of the resulting pigments to distinct λmax values is poorly understood. Rhodopsin is the only pigment with a native structure determined at high resolution. Homology models for cone pigments have been generated, but experimentally determined structures are needed for a precise understanding of spectral tuning. The principal obstacle to solving the structures of cone pigments has been their innate instability in recombinant constructs. By inserting five different thermostabilizing proteins (BRIL, T4L, PGS, RUB, and FLAV) into the recombinant green opsin sequence, constructs were created that were up to 9-fold more stable than WT. Using cellular retinaldehyde-binding protein (CRALBP), we developed a quick means of assessing the stability of the green pigment. CRALBP testing also confirmed an additional 48-fold increase in pigment stability when varying the detergent used. These results suggest an efficient protocol for routine purification and stabilization of cone pigments that could be used for high-resolution determination of their structures, as well as for other studies.

apparent that conformational reorganization coupled to the ionization of the buried group is a major determinant of these pK a values. Specifically, the creation of charge in hydrophobic environments can trigger a shift from the fully folded state to local or partially unfolded states in which the charge can gain access to water or to an environment where the charge can be solvated. These alternative conformational states are not normally populated owing to the large free energy difference between the alternative and fully-folded native states; however, the partially unfolded states can become the new ground state under pH conditions where the internal group is charged. If the ionization of an internal group promotes the transition to a new conformational state then its pK a should be sensitive to the global thermodynamic stability (DG) of the protein because this determines the energy gap between the ground and the alternative states. This was tested by measuring the pK a of two internal Lys residues in variants of staphylococcal nuclease with thermodynamic stabilities ranging from 8.4 to 13.8 kcal/mol. The magnitude of the shift in the pK a of the internal Lys residues was found to be sensitive to the DG of the protein confirming that the pK a values of these Lys residues are determined by the probability of structural reorganization more than by local dielectric properties of their microenvironments. These observations imply that structure-based pK a calculations for buried groups and other electrostatic processes in hydrophobic environments require accurate treatment of conformational reorganization, which remains an extremely challenging proposition.