Computer simulations of the dynamics of human choriogonadotropin and its alpha subunit

Rapid Maturation of Glycoprotein Hormone Free α-Subunit (GPHα) and GPHαα Homodimers

The dynamics of glycoprotein hormone α-subunit (GPHα) maturation and GPHαα homodimer formation were studied in presence (JEG-3 choriocarcinoma cells) and absence (HeLa cells) of hCGβ. In both cases, the major initially occurring GPHα variant in [35S]Met/Cys-labeled cells carried two N-glycans (Mr app = 22 kDa). Moreover, a mono-N-glycosylated in vivo association-incompetent GPHα variant (Mr app = 18 kDa) was observed. In JEG-3 cells the early 22-kDa GPHα either associated with hCGβ, or showed self-association to yield GPHαα homodimers, or was later converted into heavily glycosylated large free GPHα (Mr app = 24 kDa). Micro-preparative isolation of intracellular GPHαα homodimers of JEG-3 cells and their conversion by reduction revealed that they consisted of 22-kDa GPHα monomers and not of large free GPHα. In HeLa cells, the large free GPHα variant was not observed, whereas GPHαα homodimers were present. Intracellularly, early GPHαα homodimers (35 kDa) and late variants (JEG-3: 44 kDa, HeLa: 39 kDa) were found. Both cell types secreted 45 kDa GPHαα homodimers. Large free GPHα and GPHαα homodimers were more rapidly sialylated than hCG αβ-heterodimers indicating a sequestration mechanism in the secretory pathway. In GPHαα homo- as well as hCG αβ-heterodimers the subunit interaction site, located on loop 2 of GPHα (amino acids 33–42), became immunologically inaccessible indicating similar spatial orientation of GPHα in both types of dimers. The studies demonstrate the formation, in vivo dynamics of GPHαα homodimers, and the pathways of the cellular metabolism of variants of GPHα, monoglycosylated GPHα and large free GPHα.

A Prototype Manipulator for Magnetic Resonance-Guided Interventions Inside Standard Cylindrical Magnetic Resonance Imaging Scanners

The aim of this work is to develop a remotely controlled manipulator to perform minimally invasive diagnostic and therapeutic interventions in the abdominal and thoracic cavities, with real-time magnetic resonance imaging (MRI) guidance inside clinical cylindrical MR scanners. The manipulator is composed of a three degree of freedom Cartesian motion system, which resides outside the gantry of the scanner, and serves as the holder and global positioner of a three degree of freedom arm which extends inside the gantry of the scanner At its distal end, the arm's end-effector can carry an interventional tool such as a biopsy needle, which can be advanced to a desired depth by means of a seventh degree of freedom. These seven degrees of freedom, provided by the entire assembly, offer extended manipulability to the device and a wide envelope of operation to the user, who can select a trajectory suitable for the procedure. The device is constructed of nonmagnetic and nonconductive fiberglass, and carbon fiber composite materials, to minimize artifacts and distortion on the MR images as well as eliminate effects on its operation from the high magnetic field and the fast switching magnetic field gradients used in MR imaging. A user interface was developed for man-in-the-loop control of the device using real-time MR images. The user interface fuses all sensor signals (MR and manipulator information) in a visualization, planning, and control command environment. Path planning is performed with graphical tools for setting the trajectory of insertion of the interventional tool using multislice and/or three dimensional MR images which are refreshed in real time. The device control is performed with an embedded computer which runs real-time control software. The manipulator compatibility with the MR environment and image-guided operation was tested on a 1.5 T MR scanner.