Molecular investigation of the tandem Tudor domain and plant homeodomain histone binding domains of the epigenetic regulator UHRF2

Ubiquitin-like containing PHD and ring finger (UHRF)1 and UHRF2 are multidomain epigenetic proteins that play a critical role in bridging crosstalk between histone modifications and DNA methylation. Both proteins contain two histone reader domains, called tandem Tudor domain (TTD) and plant homeodomain (PHD), which read the modification status on histone H3 to regulate DNA methylation and gene expression. To shed light on the mechanism of histone binding by UHRF2, we have undergone a detailed molecular investigation with the TTD, PHD and TTD-PHD domains and compared the binding activity to its UHRF1 counterpart. We found that unlike UHRF1 where the PHD is the primary binding contributor, the TTD of UHRF2 has modestly higher affinity toward the H3 tail, while the PHD has a weaker binding interaction. We also demonstrated that like UHRF1, the aromatic amino acids within the TTD are important for binding to H3K9me3 and a conserved aspartic acid within the PHD forms an ionic interaction with R2 of H3. However, while the aromatic amino acids in the TTD of UHRF1 contribute to selectivity, the analogous residues in UHRF2 contribute to both selectivity and affinity. We also discovered that the PHD of UHRF2 contains a distinct asparagine in the H3R2 binding pocket that lowers the binding affinity of the PHD by reducing a potential electrostatic interaction with the H3 tail. Furthermore, we demonstrate the PHD and TTD of UHRF2 cooperate to interact with the H3 tail and that dual domain engagement with the H3 tail relies on specific amino acids. Lastly, our data indicate that the unique stretch region in the TTD of UHRF2 can decrease the melting temperature of the TTD-PHD and represents a disordered region. Thus, these subtle but important mechanistic differences are potential avenues for selectively targeting the histone binding interactions of UHRF1 and UHRF2 with small molecules.

[Primary epiphyseal osteomyelitis in children]

A 4-year-old boy was hospitalized for suspected hematogenous osteomyelitis of the distal femur. Bone scan and repeated radiographs showed a rare condition, primary epiphyseal osteomyelitis. Needle biopsy and aspiration were negative. Penbritin and orbenil, 2 g of each, gave complete clinical and radiographic healing 7 weeks after initial treatment.

Early diagnosis at the CDH clinic

In 1978, 488 of 8,211 registered newborn babies in the Haifa area were referred to us for suspected congenital dislocation of the hip. The findings were as follows: normal, 53%; justifying further follow-up, 40.5%; subluxation, 4% (19 cases); and dislocation, 2.5% (12 cases). The infants with subluxation or dislocation were not older than six months. Treatment of dislocation included: open reduction, 1; closed reduction under general anesthesia, 4; and reduction and treatment by abduction splints, 7. After this treatment, all hips were stable. Abduction splints were used in the 19 subluxation cases; there was no aseptic necrosis of the femoral head. All infants with minor deviations in the hip joints, such as consistent limited abduction, delayed appearance of epiphyseal ossification center or acetabular dysplasia, were deliberately grouped under "justifying follow-up." It is possible that these minor deviations harbor the buds of early osteoarthritis.