Tal, a Tsg101-specific E3 ubiquitin ligase, regulates receptor endocytosis and retrovirus budding.

The tumor suppressor gene 101 (tsg101) regulates vesicular trafficking processes in yeast and mammals. We report a novel protein, Tal (Tsg101-associated ligase), whose RING finger is necessary for multiple monoubiquitylation of Tsg101. Bivalent binding of Tsg101 to a tandem tetrapeptide motif (PTAP) and to a central region of Tal is essential for Tal-mediated ubiquitylation of Tsg101.

Detection of ERK activation by a novel monoclonal antibody.

The mitogen-activated protein kinase, ERK is activated by a dual phosphorylation on threonine and tyrosine residues. Using a synthetic diphospho peptide, we have generated a monoclonal antibody directed to the active ERK. The antibody specifically identified the active doubly phosphorylated, but not the inactive mono- or non- phosphorylated forms of ERKs.

A novel, mild, specific and indirect maleimido-based radioiodolabeling method. Radiolabeling of analogs derived from parathyroid hormone (PTH) and PTH-related protein (PTHrP).

In an effort to design a mild, non-oxidative and site-specific means of radiolabeling bioactive molecules we have employed maleimido-sulfhydryl chemistry to produce bioactive hormone radioligands. We have prepared two novel radioiodolabeled reagents, 3'-maleimidopropanoyl-3-125I-tyramide and its retro analog, N-maleoyl-N'-3-(4-hydroxy-3-125I-phenyl)propanoyl ethylenediamide, by either oxidative radioiodination of the precursors or radiolabeling of the phenolic component prior to its incorporation into the radiolabeling reagents. These reagents were then used to radiolabel analogs of parathyroid hormone (PTH) and parathyroid hormone-related protein (PTHrP) in an efficient way, yielding reaction mixtures which were easily purified.

Synthesis of fully active biotinylated analogues of parathyroid hormone and parathyroid hormone-related protein as tools for the characterization of parathyroid hormone receptors.

The synthesis, purification, and characterization of biotinylated analogues of parathyroid hormone (PTH) and PTH-related protein (PTHrP) are described. A novel methodology was developed which allowed the selective biotinylation during solid-phase synthesis of either the Lys13 or Lys26 residue in PTH/PTHrP sequences. Incorporation of orthogonally protected N alpha-Boc-Lys(N epsilon-Fmoc) at a selected position in the sequence, followed by selective side-chain deprotection and biotinylation of the epsilon-amino group, permitted modification of the specific lysine only.

Pseudopeptide analogues of substance P and leucine enkephalinamide containing the psi (CH2O) modification: synthesis and biological activity.

The isosteric methyleneoxy psi (CH2O) function was employed as a novel peptide-bond surrogate and incorporated into sequences of two neuropeptides, substance P (SP) and enkephalin. A pseudopeptide analogue [pGlu6,Phe8 psi(CH2O)Gly9]SP6-11 (7) of SP related C-terminal hexapeptide [pGlu6]SP6-11 and two pseudopeptide analogues of [Leu5]enkephalinamide, [Tyr1 psi (CH2O)Gly2, Leu5] enkephalinamide (11) and [Gly2 psi (CH2O)-Gly3, Leu5]enkephalinamide (17), were synthesized. The N alpha-protected pseudodipeptidic units were incorporated in the appropriate peptide sequences by using conventional coupling methods in solution.