Substitution of a single residue in Stichodactyla helianthus peptide, ShK-Dap22, reveals a novel pharmacological profile.
ShK, a peptide isolated from Stichodactyla helianthus venom, blocks the voltage-gated potassium channels, K(v)1.1 and K(v)1.3, with similar high affinity. ShK-Dap(22), a synthetic derivative in which a diaminopropionic acid residue has been substituted at position Lys(22), has been reported to be a selective K(v)1.3 inhibitor and to block this channel with equivalent potency as ShK [Kalman et al. (1998) J. Biol. Chem. 273, 32697-32707]. In this study, a large body of evidence is presented which indicates that the potencies of wild-type ShK peptide for both K(v)1.3 and K(v)1.1 channels have been previously underestimated. Therefore, the affinity of ShK-Dap(22) for both channels appears to be ca. 10(2)-10(4)-fold weaker than ShK. ShK-Dap(22) does display ca. 20-fold selectivity for human K(v)1.3 vs K(v)1.1 when measured by the whole-cell voltage clamp method but not in equilibrium binding assays. ShK-Dap(22) has low affinity for K(v)1.2 channels, but heteromultimeric K(v)1.1-K(v)1.2 channels form a receptor with ca. 200-fold higher affinity for ShK-Dap(22) than K(v)1.1 homomultimers. In fact, K(v)1.1-K(v)1.2 channels bind ShK-Dap(22) with only ca. 10-fold less potency than ShK and reveal a novel pharmacology not predicted from the homomultimers of K(v)1.1 or K(v)1.2. The concentrations of ShK-Dap(22) needed to inhibit human T cell activation were ca. 10(3)-fold higher than those of ShK, in good correlation with the relative affinities of these peptides for inhibiting K(v)1.3 channels. All of these data, taken together, suggest that ShK-Dap(22) will not have the same in vivo immunosuppressant efficacy of other K(v)1.3 blockers, such as margatoxin or ShK. Moreover, ShK-Dap(22) may have undesired side effects due to its interaction with heteromultimeric K(v)1.1-K(v)1.2 channels, such as those present in brain and/or peripheral tissues.
Middleton
Richard E
RE
Department of Ion Channels, Merck Research Laboratories, P.O. Box 2000, Rahway, New Jersey 07065, USA.
Sanchez
Manuel
M
Linde
Ana-Rosa
AR
Bugianesi
Randal M
RM
Dai
Ge
G
Felix
John P
JP
Koprak
Sam L
SL
Staruch
Mary Jo
MJ
Bruguera
Marc
M
Cox
Rachael
R
Ghosh
Amrita
A
Hwang
Jeremy
J
Jones
Simmonette
S
Kohler
Martin
M
Slaughter
Robert S
RS
McManus
Owen B
OB
Kaczorowski
Gregory J
GJ
Garcia
Maria L
ML
D019943:Amino Acid Substitution; D000818:Animals; D001921:Brain / Q000378:metabolism; D016466:CHO Cells; D002460:Cell Line; D003064:Cnidarian Venoms / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology*; D006224:Cricetinae; D006801:Humans; D020128:Inhibitory Concentration 50; D008564:Membrane Potentials / Q000187:drug effects; D009865:Oocytes / Q000378:metabolism; D010455:Peptides / Q000737:chemistry* / Q000235:genetics / Q000494:pharmacology*; D026902:Potassium Channel Blockers / Q000737:chemistry / Q000494:pharmacology*; D015221:Potassium Channels / Q000187:drug effects / Q000502:physiology; D011869:Radioligand Assay; D012615:Sea Anemones / Q000737:chemistry; D013329:Structure-Activity Relationship; D013601:T-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D014981:Xenopus
D003064:Cnidarian Venoms; D010455:Peptides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; C095391:ShK neurotoxin