The cystatin superfamily consists of a large group of cystatin domain-containing proteins, most of which are reversible and tight-binding inhibitors
of the papain (C1) and legumain (C13) families of cysteine proteases [1,E1].
Kininogens are multifunctional and multidomain glycoproteins related to
cystatins. Kininogens ubiquitously exist in vertebrates, including mammals,
birds, amphibians, and fishes. They vary extremely in both structure and
function among different taxa of animals, in particular between mammals and
amphibians. Kininogens contain a bradykinin domain and one (in lampreys), two
(in fishes) or three (in mammals, birds, and amphibians) cystatin domain(s).
Although mammalian kininogens harbor three cystatin domains only two of them
are tight-binding inhibitors of cysteine cathepsins, which belong to the
papain-like cysteine proteases. A Q-x-V-x-G motif is the canonical binding
site for cysteine proteinases in mammals [2,3,4].
The profile we developed cover the entire kininogen-type cystatin domain.
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