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Mistletoe lectin I forms a double trefoil structure
Author(s) -
Sweeney Edel C,
Tonevitsky Alexander G,
Palmer Rex A,
Niwa Hidie,
Pfueller Uwe,
Eck Juergen,
Lentzen Hans,
Agapov Igor I,
Kirpichnikov Mikhail P
Publication year - 1998
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/s0014-5793(98)00766-2
Subject(s) - ricin , dimer , protein quaternary structure , lectin , molecular replacement , stereochemistry , chemistry , crystallography , molecule , fast protein liquid chromatography , trefoil , ribosome inactivating protein , biology , ribosome , crystal structure , biochemistry , protein subunit , rna , enzyme , organic chemistry , agronomy , toxin , gene
The quaternary structure of mistletoe lectin I (MLI), a type II ribosome inactivating protein, has been determined by X‐ray crystallography. A definitive molecular replacement solution was determined for MLI using the co‐ordinates of the homologue ricin as a search model. MLI exists as an [AB] 2 dimer with internal crystallographic two‐fold symmetry. Domain I of the B chains is non‐covalently associated through interactions involving three looped chains (α, β, γ) in each molecule of the dimer, forming a double trefoil structure. The ricin molecule which shares 52% sequence homology with MLI has a disulphide bridge between Cys 20 and Cys 39 in the α loop. An evolutionary mutation has replaced Cys 39 with serine in MLI. This mutation appears to allow the α loop the flexibility required to take up its place at the dimer interface, and also suggests a rationale for why ricin does not form dimers. Measurement of retention times using FPLC gel filtration confirms that dimerisation also occurs in solution between MLI B chains with an association constant K a =10 6 M.