Identification and three-dimensional structural analysis of nine novel mutations in patients with prothrombin deficiency

Prothrombin deficiency is an autosomal recessive disorder associated with a moderately severe bleeding tendency. In this study, 13 patients with proth rombin deficiency were screened for the presence of alterations in the prot hrombin gene, and nine novel candidate mutations were identified. Of 11 pat ients with hypoprothrombinemia, ten are homozygous for five mutations and o ne patient is a compound heterozygote. The two patients with dysprothrombin emia are homozygous for two mutations. Eight of nine mutations are missense ones associated with single amino acid substitutions in the propeptide (Ar g-1Gln, Arg-2Trp), the kringle-1(Asp118Try) and kringle-2 (Arg220Cys) domai ns and the catalytic serine protease domain (Gly330Ser, Ser354Arg, Arg382Hi s and Arg538Cys). The ninth mutation is an in-frame deletion of 3 bp that r esults in the omission of one amino acid (del Lys 301/302). The combination of these missense mutations with crystal structures for alpha -thrombin an d the prothrombin fragments 1 and 2 resulted in new insight into the functi on of a-thrombin. The hypoprothrombinemia mutations were inferred to affect either the cleavage of the propeptide from the cia domain, the stability o f the kringle-l and -2 domains, or the close association of the A and B cha ins of the serine protease domain. The dysprothrombinemia mutations were in ferred to directly affect catalytic function through their location at the active site crevice or exosite 1 within the serine protease domain.