Linear and cyclic peptide analogues of the polypeptide cardiac stimulant, anthopleurin‐A

Abstract

A loop corresponding to residues 8–17 in the polypeptide cardiac stimulant anthopleurin‐A is known to be important for the cardiostimulant activity of this molecule. To investigate the activity and possible conformations of this loop in isolation, two synthetic peptides have been studied. The first corresponds to residues 6–20 of anthopleurin‐A with Cys6 replaced by Thr, and the second to residues 6–21 of anthopleurin‐A, with Thr21 replaced by Cys. The introduction of an additional cysteine in the latter peptide enabled an intramolecular disulfide to be formed between the N‐ and C‐terminal residues. Both linear peptides and the disulfide‐containing analogue lack the cardiostimulant and Na+‐channel binding activity of the parent molecule, anthopleurin‐A, indicating that although the loop is important for the function of anthopleurin‐A, other regions of the molecule must also be involved in activity. Assignments of the 1H‐NMR spectra of both peptides are presented, and their pH and temperature dependences investigated. The results show that the amide protons of Gly5 and Asn11 (corresponding to Gly10 and Asn16 in anthopleurin‐A) sample hydrogen‐bonded conformations in solution. Based on these NMR data, two regions of non‐random structure, encompassing residues 2–5 and 8–11, respectively, are proposed, and the possible involvement of such structures in the activity of anthopleurin‐A is discussed.

Solution structure of a defensin-like peptide from platypus venom

“…All cysteine residues found to be topologically equivalent by the DALI algorithm were disulphide-bonded in an identical fashion in each molecule. The anti-parallel β-strands in DLP-1 (15)(16)(17)(18)(37)(38)(39)(40) correspond closely with those in β-defensin-12 (10)(11)(12)(13)(32)(33)(34)(35)(36), although one of the strands in the latter is longer by one residue. Part of the large loop in DLP-1, defined by residues 24-27 and 30-36, corresponds to the region in β-defensin-12 defined by residues 21-31, which contains a β-strand and a βbulge.…”

“…The results showed that DLP-1, which is characterized by a 1-5, 2-4 and 3-6 disulphide connectivity and CX ' CX ( CX ( CX ' CCX # pattern, had some similarities with the sea anemone toxins ShI, ATX-II and AP-A, (CXCX #! -## CX ' CX ) -* CCX) [39] and rattlesnake myotoxins (X $ CX ' CX ' CX "" CX & CCX % -( ) [40,41]. As mentioned earlier, the DALI search had indicated that ShI, which has a similar tertiary fold to that of ATX-II and AP-A, is structurally similar to DLP-…”

Solution structure of the cardiostimulant polypeptide anthopleurin-B and comparison with anthopleurin-A

“…Thus, the minor changes in chemical shift appear to correlate roughly with changes in the hydrogen-bonding network in this region of the protein. In linear and cyclized synthetic peptides incorporating this region of the sequence of AP-A, the amide of GlylO was shifted upfield by 0.18 ppm and 0.23 ppm, respectively, but the Asp9 amide had close to random coil chemical shifts [27]. In the case of GlylO, this suggests that similar structures to those in the intact proteins are populated in the isolated peptides and supports the notion that the chemical shift perturbations of GlylO in AP-A and AP-B reflect local interactions.…”

Solution structure of a defensin-like peptide from platypus venom

“…All cysteine residues found to be topologically equivalent by the DALI algorithm were disulphide-bonded in an identical fashion in each molecule. The anti-parallel β-strands in DLP-1 (15)(16)(17)(18)(37)(38)(39)(40) correspond closely with those in β-defensin-12 (10)(11)(12)(13)(32)(33)(34)(35)(36), although one of the strands in the latter is longer by one residue. Part of the large loop in DLP-1, defined by residues 24-27 and 30-36, corresponds to the region in β-defensin-12 defined by residues 21-31, which contains a β-strand and a βbulge.…”