AJP - Cell Physiology, Vol 271, Issue 3 C736-C741, Copyright © 1996 by American Physiological Society
Positive charge modifications alter the ability of XIP to inhibit the plasma membrane calcium pump
W. Xu, C. Gatto and M. A. Milanick
Department of Physiology, School of Medicine, University of Missouri-Columbia 65212, USA.
Exchange inhibitory peptide (XIP; RRLLFYKYVYKRYRAGKQRG) is the shortest
peptide that inhibits the plasma membrane Ca pump at high Ca (A. Enyedi, T.
Vorherr, P. James, D. J. McCormick, A. G. Filoteo, E. Carafoli, and J. T.
Penniston, J. Biol. Chem. 264: 12313-12321, 1989). Sulfosuccinimidyl
acetate (SNA)-modified XIP does not inhibit the Ca pump; SNA neutralizes
the positive charge on Lys at positions 7, 11, and 17. Peptide 2CK-XIP
(RRLLFYRYVYRCYCAGRQKG) inhibits the pump, but the iodoacetamido-modified
peptide does not inhibit. Three peptide analogues, in which 7, 11, and 17
were Ala, Cys, or Lys, inhibited about as well as XIP. SNA modification of
these analogues (each with 1 Lys) did not inhibit. SNA modification of
2CK-XIP results in a peptide that does not inhibit; thus position 19 is
important. Our results suggest that it is critical that position 19 be
positively charged, that positions 7, 11, and 17 are important contact
points between XIP and the Ca pump (with at least one positively charged),
and that, whereas it is not essential that residues 12 and 14 be positive,
they cannot be negative.
