Structure of a protein G helix variant suggests the importance of helix propensity and helix dipole interactions in protein design.

Six helix surface positions of protein G (Gbeta1) were redesigned using a computational protein design algorithm, resulting in the five fold mutant Gbeta1m2. Gbeta1m2 is well folded with a circular dichroism spectrum nearly identical to that of Gbeta1, and a melting temperature of 91 degrees C, approximately 6 degrees C higher than that of Gbeta1. The crystal structure of Gbeta1m2 was solved to 2.0 A resolution by molecular replacement. The absence of hydrogen bond or salt bridge interactions between the designed residues in Gbeta1m2 suggests that the increased stability of Gbeta1m2 is due to increased helix propensity and more favorable helix dipole interactions.

Composite adenocarcinoma and carcinoid tumor of urinary bladder.

We present a unique case of primary mixed adenocarcinoma of the urinary bladder consisting of signet-ring cells, glands, and mucinous lakes intimately associated with carcinoid elements. Neuroendocrine differentiation was substantiated with immunohistochemical and ultrastructural studies. The literature on primary carcinoid tumor of the bladder is reviewed.