Delimiting the autoinhibitory module of von Willebrand factor.

Essentials The self-inhibitory mechanism of von Willebrand factor (VWF) remains unclear. Residues flanking the A1 domain of VWF form a discontinuous autoinhibitory module (AIM). rVWF1238-1493 exhibited greater thermostability and inactivity than its shorter counterparts. The cooperative coupling between the N- and C- AIM regions are required for inhibiting A1. SUMMARY: Background The hierarchical hemostasis response involves a self-inhibitory feature of von Willebrand factor (VWF) that has not been fully characterized. The residues flanking the A1 domain of VWF are important in this self-inhibition by forming an autoinhibitory module (AIM) that masks the A1 domain. Objectives To delimit the AIM sequence and to evaluate the cooperative interplay between the discontinuous AIM regions. Methods ELISA, flow cytometry, a thermal stability assay and hydrogen-deuterium exchange (HDX) mass spectrometry were used to characterize recombinant VWF A1 fragments varying in length. Results The longest A1 fragment (rVWF1238-1493 ) showed higher inactivity in binding the platelet receptor glycoprotein (GP) Ibα and greater thermostability than its shorter counterparts. The HDX results showed that most of the N-terminal residues and residues 1459-1478 at the C-terminus of rVWF1238-1493 have slower deuterium uptake than the residues in its denatured counterpart, implying that these residues may interact with the A1 domain. In contrast, residues 1479-1493 showed less difference from the denatured form, indicating that these residues are unlikely to be involved in binding the A1 domain. The A1 fragment that lacks either the entire C-terminal flanking region of the AIM (C-AIM), i.e. rVWF1238-1461 , or the entire N-terminal flanking region of the AIM (N-AIM), i.e. rVWF1271-1493 , showed high GPIbα-binding affinity and low thermostability, suggesting that removal of either N-terminal or C-terminal residues resulted in loss of AIM inhibition of the A1 domain. Conclusion The AIM is probably composed of residues 1238-1271 (N-AIM) and 1459-1478 (C-AIM). Neither the N-AIM nor the C-AIM alone could fully inhibit binding of the A1 domain to GPIbα.

Intra-familial transmission of life-threatening group A streptococcal infection.

Invasive group A streptococcal (GAS) infections have been of increasing concern worldwide during the past 15 years. Spread of group A streptococci to contacts with resulting invasive infection has been reported in families, in residential nursing homes, and even from patients to health care workers. We report an instance of temporally related life-threatening group A streptococcal infection in a husband and 2 weeks later in his wife. This example further emphasizes the need for careful observation among family members and other close contacts of patients with invasive group A streptococcal infection. Although at present there are no universal recommendations for monitoring or for antibiotic prophylaxis of close contacts of persons with invasive GAS infection, when added to existing literature, this report suggests additional consideration is required.

Positive direct antiglobulin tests at birth without demonstrable maternal antibody.

A healthy 38-year-old white woman had two abortions and three live children. Red cells from each of her living children at birth had a strongly positive direct antiglobulin test. Detailed studies on the third child showed that the cells were sensitized by IgG. Maternal serum, tested by a range of techniques against reagent red cells and the husband's cells, showed no unusual antibody. Maternal serum and eluates prepared from red cells of the third child did not react with fresh cells from the older siblings (aged 7 and 10 years). Follow-up on the third child showed that the direct antiglobulin test was positive at 2 months, weakly positive at 4 months, and negative at 8 months. Red cells collected at 8 months of age did not react with the stored eluate prepared from the baby's sensitized red cells at birth. The most likely explanation of these data is that the children inherited a paternal antigen that is only present as a red cell surface-active structure during fetal development.

Benzo(a)pyrene in gasoline partially persists in automobile exhaust.

On average 36 percent of the benzo[a]pyrene in an automobile's exhaust gas comes from the benzo[a]pyrene originally in the gasoline. Between 0.1 and 0.2 percent of the benzo[a]pyrene in the gasoline survives the combustion process and is recovered from the exhaust; 5 percent accumulates in the crankcase oil. Some of the benzo[a]pyrene in the gasoline is converted into other polynuclear aromatic hydrocarbons and other more polar compounds. For our experiments we used commercial gasoline containing benzo[a]pyrene at 1.0 part per million to which was added benzo[a]pyrene-8,9-(14)C at 1.1 parts per million as a radioactive tracer.