Synthesis and NMR Characterization of the Prenylated Peptide, a-Factor.

Protein and peptide prenylation is an essential biological process involved in many signal transduction pathways. Hence, it plays a critical role in establishing many major human ailments, including Alzheimer's disease, amyotrophic lateral sclerosis (ALS), malaria, and Ras-related cancers. Yeast mating pheromone a-factor is a small dodecameric peptide that undergoes prenylation and subsequent processing in a manner identical to larger proteins. Due to its small size in addition to its well-characterized behavior in yeast, a-factor is an attractive model system to study the prenylation pathway. Traditionally, chemical synthesis and characterization of a-factor have been challenging, which has limited its use in prenylation studies. In this chapter, a robust method for the synthesis of a-factor is presented along with a description of the characterization of the peptide using MALDI and NMR. Finally, complete assignments of resonances from the isoprenoid moiety and a-factor from COSY, TOCSY, HSQC, and long-range HMBC NMR spectra are presented. This methodology should be useful for the synthesis and characterization of other mature prenylated peptides and proteins.

Development of a Highly Active Fluorescence-Based Detector for Yeast G Protein-Coupled Receptor Ste2p.

Twenty analogs of [Orn6,D-Ala9]α-factor were synthesized and assayed for their biological activities: seven analogs of [Orn6,X9]α-factor, seven analogs of [X6,D-Ala9]α-factor, five analogs of [X5,X6,D-Ala9]α-factor, and native α-factor (X = amino acids). Their biological activities (halo, gene induction, and affinity) were measured using S. cerevisiae Y7925 and LM102 and compared with those of native α-factor (100%). G protein-coupled receptor was expressed in strain LM102 containing pESC-LEU-STE2 vector. [Dap6,D-Ala9]α-factor with weak halo activity (10%) showed the highest receptor affinity (＞ 230%) and the highest gene induction activity (167%). [Arg6,D-Ala9]α-factor showed the highest halo activity (2,000%). The number of active binding sites per cell (about 20,000 for strain LM102) was determined using a newly-designed fluorescence-based detector, [Arg6,D-Ala9]α-factor-Edan, with high sensitivity (12,500-fold higher than the absorption-based detector [Orn6]α-factor-[Cys]3).

a-Factor Analogues Containing Alkyne- and Azide-Functionalized Isoprenoids Are Efficiently Enzymatically Processed and Retain Wild-Type Bioactivity.

Protein prenylation is a post-translational modification that involves the addition of one or two isoprenoid groups to the C-terminus of selected proteins using either farnesyl diphosphate or geranylgeranyl diphosphate. Three crucial enzymatic steps are involved in the processing of prenylated proteins to yield the final mature product. The farnesylated dodecapeptide, a-factor, is particularly useful for studies of protein prenylation because it requires the identical three-step process to generate the same C-terminal farnesylated cysteine methyl ester substructure present in larger farnesylated proteins. Recently, several groups have developed isoprenoid analogs bearing azide and alkyne groups that can be used in metabolic labeling experiments. Those compounds have proven useful for profiling prenylated proteins and also show great promise as tools to study how the levels of prenylated proteins vary in different disease models. Herein, we describe the preparation and use of prenylated a-factor analogs, and precursor peptides, to investigate two key questions. First, a-factor analogues containing modified isoprenoids were prepared to evaluate whether the non-natural lipid group interferes with the biological activity of the a-factor. Second, a-factor-derived precursor peptides were synthesized to evaluate whether they can be efficiently processed by the yeast proteases Rce1 and Ste24 as well as the yeast methyltransferase Ste14 to yield mature a-factor analogues. Taken together, the results reported here indicate that metabolic labeling experiments with azide- and alkyne-functionalized isoprenoids can yield prenylated products that are fully processed and biologically functional. Overall, these observations suggest that the isoprenoids studied here that incorporate bio-orthogonal functionality can be used in metabolic labeling experiments without concern that they will induce undesired physiological changes that may complicate data interpretation.

Synthesis of methyl 4-dihydrotrisporate B and methyl trisporate B, morphogenetic factors of Zygomycetes fungi.

(9Z)-Methyl 4-dihydrotrisporate B and (9Z)-methyl trisporate B, pheromones of Zygomycetes fungi, have been synthesized using Stille cross-coupling from previously described cyclohexenone precursors. Conducting the coupling without protection groups allowed for a short and stereospecific synthesis route of the late trisporoids. Stability studies for both the compounds revealed (9Z)-methyl trisporate B to be very unstable against UV irradiation.