Jochen Walter

Structure of bovine pancreatic trypsin inhibitor. Results of joint neutron and X-ray refinement of crystal form II

The structure of form II crystals of bovine pancreatic trypsin inhibitor has been investigated by joint refinement of X-ray and neutron data. Crystallographic R factors for the final model were 0.200 for the X-ray data extending to 1 A resolution and 0.197 for the 1.8 A neutron data. This model was strongly restrained, with 0.020 A root-mean-square (r.m.s.) departure of bond lengths from their ideal values and 0.019 A r.m.s. departure of planar groups from planarity. The resulting structure was very similar to that of crystal form I (r.m.s. deviation for main chain atoms was 0.40 A); nevertheless larger deviations were observed in particular regions of the chain. Twenty out of 63 ordered water molecules occupy similar positions (deviation less than 1 A) in both models. Eleven amide hydrogens were found to be protected from exchange after three months of soaking the crystals in deuterated mother liquor at pH 8.2. Their locations were in excellent agreement with the results obtained by two-dimensional nuclear magnetic resonance, but the rates of exchange are much lower in the crystalline state.

A common denominator of growth cone guidance and collapse

Axonal guidance in the retinotectal system and in spinal nerve segmentation is based on repulsion or inhibition. In both systems the membrane glycoprotein responsible for the guiding activity is capable of inducing growth cone collapse. We discuss two models of axonal guidance that correlate axonal guidance and growth cone collapse. The models are applicable to axon guidance by membrane-associated or diffusible stimuli, and are not based on preferential adhesion of axons to certain substrata.

Pancreatic trypsin inhibitor: A new crystal form and its analysis

Basic pancreatic trypsin inhibitor (Trasylol) was crystallized in a new crystal form with space group P212121 and lattice constants a = 74.1 A, b = 23.4 A, c = 28.9 A. Its structure was determined at 0.94 A resolution applying Patterson search techniques.

Molecular mechanisms separating two axonal pathways during embryonic development of the avian optic tectum

During embryonic development of the avian optic tectum, retinal and tectobulbar axons form an orthogonal array of nerve processes. Growing axons of both tracts are transiently very closely apposed to each other. Despite this spatial proximity, axons from the two pathways do not intermix, but instead restrict their growth to defined areas, thus forming two separate plexiform layers, the stratum opticum and the stratum album centrale. In this study we present experimental evidence indicating that the following three mechanisms might play a role in segregating both axonal populations: Retinal and tectobulbar axons differ in their ability to use the extracellular matrix protein laminin as a substrate for axonal elongation; the environment in the optic tectum is generally permissive for retinal axons, but is specifically nonpermissive for tectobulbar axons, resulting in a strong fasciculation of the latter; and growth cones of temporal retinal axons are reversibly inhibited in their motility by direct contact with the tectobulbar axons membrane.

Is guidance of chick retinal axons in vitro influenced by proteases

Rhodamine-labeled explants of embryonic chick retinae were placed on a substratum consisting of alternating lanes of cell membranes derived from anterior and posterior chick optic tectum. Extending axons from temporal retinae prefer to grow in vitro on anterior tectal membranes because of a repulsive component within posterior membranes obtained from a tectum area which is not innervated by these axons in vivo. None of 16 protease inhibitors, specific for all known protease classes, when added to the culture medium, neutralized the repulsive activity of posterior membranes suggesting that the repulsive activity is not a protease. However, 2 metalloprotease inhibitors affect growth cone morphology and axon-axon interactions.

Guidance of Chick Retinal Axons in Vitro

To understand the mechanism of axonal guidance, the behavior of growing axons has been studied in several in vitro systems (Gundersen and Barrett, 1979; Lumsden and Davies, 1983; Kapfhammer et al., 1986; for review see Bray and Hollenbeck, 1988).