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D J Staples

Publications and source records attributed to D J Staples.

24 records · Page 2Linked to original sources
PubMed1987

alpha-Melanotropin: the minimal active sequence in the frog skin bioassay.

The minimal sequence required for biological activity of alpha-MSH (alpha-melanotropin, alpha-melanocyte stimulating hormone) was determined in the frog (Rana pipiens) skin bioassay. The sequence required to elicit measurable biological activity was the central tetrapeptide sequence, Ac-His-Phe-Arg-Trp-NH2 (Ac-alpha-MSH6-9-NH2), which was about 6 orders of magnitude less potent than the native tridecapeptide. Smaller fragments of this sequence (Ac-His-Phe-NH2, Ac-Phe-Arg-NH2, Ac-His-Phe-Arg-NH2) were devoid of melanotropic activity at concentrations as high as 10(-4) M. We were unable to demonstrate biological activity for the tetrapeptide, Ac-Phe-Arg-Trp-Gly-NH2 (Ac-alpha-MSH7-10-NH2), and for several carboxy terminal analogues including Ac-Lys-Pro-Val-NH2 (Ac-alpha-MSH11-13-NH2). We prepared a series of fragment analogues of alpha-MSH in an attempt to determine the contribution of each individual amino acid to the biological activity of the native hormone. The minimal potency of Ac-alpha-MSH6-9-NH2 could be enhanced about a factor of 16 by the addition of glycine to the C-terminus, yielding Ac-alpha-MSH6-10-NH2 (Ac-His-Phe-Arg-Trp-Gly-NH2). Addition of glutamic acid to the N-terminus provided the peptide, Ac-alpha-MSH5-10-NH2, which was only slightly more potent than Ac-alpha-MSH6-10-NH2, indicating that position 5 contributes little to the biological potency of alpha-MSH in this assay. Addition of methionine to the N-terminus of Ac-alpha-MSH5-10-NH2 resulted in the heptapeptide, Ac-alpha-MSH4-10-NH2, which was only about 4-fold more potent than Ac-alpha-MSH5-10-NH2. Addition of lysine and proline to the C-terminal of the Ac-alpha-MSH4-10-NH2 sequence yielded the peptide, Ac-alpha-MSH4-12-NH2 with a 360-fold increase in potency relative to Ac-alpha-MSH4-10-NH2. This peptide was only about 6-fold less potent than alpha-MSH. A series of Nle-4-substituted analogues also were prepared. Ac-[Nle4]-alpha-MSH4-10-NH2 was about 4 times more potent than Ac-alpha-MSH4-10-NH2. Ac-[Nle4]-alpha-MSH4-11-NH2 also was about 4 times more potent than Ac-alpha-MSH4-10-NH2, demonstrating that lysine-11 contributes somewhat to the biological activity of alpha-MSH on the frog skin melanocyte receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMedDate not supplied

Alpha-melanocyte stimulating hormone message and inhibitory sequences: comparative structure-activity studies on melanocytes.

We investigated the structure-activity relationships of alpha-MSH (alpha-melanocyte stimulating hormone) fragment derivatives of the generic formulae Ac-alpha-MSH(x-13)-NH2 and Ac-alpha-MSH(6-x)-NH2. The minimal C-terminal sequences required for melanotropic activity were 8-13 and 7-13, respectively, in the frog and lizard skin bioassays. The Arg8-Trp9 sequence appears to be a fundamental component of the minimal message sequences found to date such as alpha-MSH(6-9), alpha-MSH(8-13) and alpha-MSH(7-13). We discovered that Ac-alpha-MSH(7-10)-NH2 was a weak and selective alpha-MSH antagonist on the lizard skin bioassay. Analysis of alpha-MSH(7-10) analogues of the generic formula Ac-Xaa-Arg-Trp-Yaa-NH2 led to Ac-[D-Trp7,D-Phe10]alpha-MSH(7-10)-NH2, a moderately potent, specific and competitive inhibitor of alpha-MSH in both the frog and the lizard skin bioassays.

Amino Acid Sequence↗
PubMedDate not supplied

HIV protease (HIV PR) inhibitor structure-activity-selectivity, and active site molecular modeling of high affinity Leu [CH(OH)CH2]Val modified viral and nonviral substrate analogs.

This report details the structure-activity relationships of the HIV gag substrate analog Val-Ser-Gln-Asn-Leu psi[CH(OH)CH2]Val-Ile-Val (U-85548E), an inhibitor exhibiting subnanomolar affinity towards HIV type-1 aspartic proteinase (HIV-1 PR). Our data show that the P1-P2' tripeptidyl sequence provides the minimal chemical determinant for HIV-1 PR binding. We describe the structure-activity properties of Leu psi[CH(OH)CH2]Val substitution in other peptidyl ligands of nonviral substrate origin (e.g., angiotensinogen, insulin and pepstatin). Furthermore, the aspartic proteinase selectivities of a few key compounds are summarized relative to evaluation against human renin, human pepsin, and the fungal enzyme, rhizopuspepsin. These studies have led to the rational design of nanomolar potent inhibitors of both HIV-1 and HIV-2 PR. Finally, a 2.5 A resolution X-ray crystallographic structure of U-85548E complexed to synthetic HIV-1 PR dimer (Jaskolski et al., Biochemistry 30, 1600 [1991]) provided a 3-D picture of the inhibitor bound to the enzyme active site, and we performed computer-assisted molecular modeling studies to explore the possible binding modes of the above series of Leu psi[CH(OH)CH2]Val substituted HIV-1 PR inhibitors.

Amino Acid Sequence↗
PubMedDate not supplied

Effect on protein phosphatase activity of peptide backbone modification and truncation of the autoinhibitory domain peptide of calcineurin.

Solid-phase synthesis of the autoinhibitory domain of calcineurin, CaN A467-491, also produced [aspartimide477]CaN A467-491 and [iso-Asp477]CaN467-491 when Boc-based chemistry was employed. In addition, the truncated peptide CaN A467-488 was obtained when Fmoc-based chemistry was employed. All four peptides proved to be effective inhibitors of protein phosphatase activity of calcineurin. The full-length peptide and the C-terminally truncated peptide (CaN467-488) were indistinguishable, with Ki values of 28 +/- 3 and 31 +/- 5 mu M, respectively. The internally modified peptides, [iso-Asp477]CaN A467-491 and [aspartimide477]-CaN A467-491, possessed lower inhibitory potencies (Ki values of 87 +/- 10 and 55 +/- 3 mu M, respectively).

Amino Acid Sequence↗
PubMedDate not supplied

Discovery and structure-activity relationships of novel alpha-melanocyte-stimulating hormone inhibitors.

Novel D-amino acid modified, hexapeptide inhibitors of alpha-melanocyte-stimulating hormone (Ac-Ser-Tyr-Ser-Met-Glu-His-Phe-Arg-Trp-Gly-Lys-Pro-Val-NH2, alpha-MSH) are described. The discovery of the alpha-MSH inhibitory activity of a known somatotropin (growth hormone) secretagogue, H-His-D-Trp-Ala-Trp-D-Phe-Lys-NH2 ([His1, Lys6-]GHRP, I), and its chemical similarity to the alpha-MSH6-11 sequence provided the impetus to investigate the structure-activity relationships of MSH-GHRP hybrid analogues. In this study we compared the melanotropic activity of a series of peptides of the generic formula H-His-Xaa-Yaa-Trp-D-Phe-Lys-NH2 (H-[Xaa7, Yaa8, D-Phe10] alpha-MSH6-11-NH2) on the R. pipiens (frog) and A. carolinensis (lizard) skin in vitro bioassays. In summary, D-Phe7-Ala8 substitution (II) in the heptapeptide template yielded an MSH-like agonist of moderately low potency (EC50 ca. 10(-6) M) relative to alpha-MSH; D-Ala7-Ala8 substitution (III) abolished agonist or antagonist activity. alpha-MSH inhibition was effected by MSH-GHRP analogues having D-Trp7-Ala8, D-Arg7-Ala8, D-Trp7-Arg8 or Phe7-Arg8 substitutions. The D-Trp7-Ala8 and Phe7-Arg8 modified derivatives (I and VI) selectively inhibited alpha-MSH on the R. pipiens assay (pA2 = 4.7 and 5.8, respectively), as they did not possess antagonist (or agonist) activities on the A. carolinensis assay. In contrast, the D-Arg7-Ala8 and D-Trp7-Arg8 modified derivatives (IV and V) inhibited alpha-MSH on both the R. pipiens and A. carolinensis assays (pA2 values ranging 5.0-6.0).(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗