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The growing demand for liver transplantation and the concomitant scarcity of cadaveric livers have increased the need for living donor liver transplantation (LDLT). Ensuring the safety of donors and recipients is critical. The preoperative identification of the vascular and biliary tract anatomy with 3-dimensional (3D) printing may allow better preoperative surgical planning, avert unnecessary surgery in patients with potentially unsuitable anatomy, and thereby decrease the complications of liver transplant surgery. We developed a protocol and successfully 3D-printed synthetic livers (along with their complex networks of vascular and biliary structures) replicating the native livers of 6 patients: 3 living donors and 3 respective recipients who underwent LDLT. To our knowledge, these are the first complete 3D-printed livers. Using standardized preoperative, intraoperative, and postoperative assessments, we demonstrated identical anatomical and geometrical landmarks in the 3D-printed models and native livers. Three-dimensional (3D) printing is a process for making a solid 3D object of virtually any shape from a digital model. A 3D printer works as an ordinary office printer, but instead of placing a single layer of ink on paper, the machine lays down successive thin layers of a material to form a 3D object that replicates the original one. 1 The growing demand for liver transplantation and the concomitant shortage of cadaveric livers have led to a rise in living donor liver transplantation (LDLT), in which resection of the right or left liver lobe is performed for the purpose of liver transplantation. 2 Living donors are healthy individuals, so ensuring their safety is of paramount importance. There have been a number of reported donor deaths worldwide and a substantial number of donor morbidities, so there is a need for measures to optimize donor safety. 3 Many of these morbidities are attributable to incomplete preoperative anatomical characterization of vascular and biliary structures and inaccurate estimates of the liver volume; these data are needed to determine the extent of the resection. This information provides a road map, and its accuracy has improved with the introduction of radiological software able to provide 3D visualization of liver structures. 4,5 3D imaging has the ability to better demonstrate the 3D relationships between vital vascular and biliary structures and the surrounding parenchyma in comparison with conventional computed tomography (CT) or magnetic resonance imaging (MRI). 3D imaging Additional Supporting Information may be found in the online version of this article.

The presence or absence of calcium determines the activation, activity, oligomerization, and stability of blood coagulation factor XIII. To explore these observed effects, we have determined the x-ray crystal structure of recombinant factor XIII A 2 in the presence of calcium, strontium, and ytterbium. The main calcium binding site within each monomer involves the main chain oxygen atom of Ala-457, and also the side chains from residues Asn-436, Asp-438, Glu-485, and Glu-490. Calcium and strontium bind in the same location, while ytterbium binds several angstroms removed. A novel ytterbium binding site is also found at the dimer two-fold axis, near residues Asp-270 and Glu-272, and this site may be related to the reported inhibition by lanthanide metals (Achyuthan, K. E., Mary, A., and Greenberg, C. S. (1989) Biochem. J. 257, 331-338). The overall structure of ion-bound factor XIII is very similar to the previously determined crystal structures of factor XIII zymogen, likely due to the constraints of this monoclinic crystal form. We have merged the three independent sets of water molecules in the structures to determine which water molecules are conserved and possibly structurally significant.The biological importance of factor XIII (fXIII) 1 (EC 2.3.2.13) lies in its ability to form new covalent bonds between protein chains. This activity was first recognized while studying blood coagulation; fXIII was required to form an insoluble clot (1). The activated form of fXIII covalently cross-links two fibrin molecules via an isopeptide bond between the side chains of a glutamine and a lysine located in the C-terminal region of the ␥-chain. Over a longer time period in coagulation, it also forms cross-links between the ␣-and ␥-chains of fibrin (2), and between ␣ 2 -anti-plasmin and fibrin (3). fXIII has been shown to react with more than fibrin (4), and it has recently been found in brain tumors (5) and arthritic joints (6), and there are cases of fXIII deficiencies (7,8). Factor XIII is a member in the family of transglutaminases (TGases), which have a wide range of biological functions (9).Like most coagulation factors, fXIII is synthesized as a zymogen and then cleaved by a protease to become an active enzyme. The structure of fXIII zymogen was determined several years ago (10, 11). In this crystal form, the active site cysteine, Cys-314, is inaccessible to solvent and is not available for catalysis.Physiologically, calcium ions are required for fXIII activation and for TGase activity. In the blood, activation of circulating fXIII requires thrombin cleavage, calcium ions (1.5 mM) (12-14), and fibrin(ogen) (15). High levels of calcium (Ͼ50 mM) can activate fXIII without the use of thrombin (15), and it has recently been shown that platelet fXIII can be activated nonproteolytically in vivo (16).Based on the amino acid sequence, the calcium binding site was predicted to be in a region (residues 468 -479) with high similarity to the EF-hand motif (17, 18). The main calcium binding site, as seen in the preliminary cryst...

Abstract:The X-ray crystal structure of human transglutaminase factor XI11 has revealed a cysteine proteinase-like active site involved in a crosslinking reaction and not proteolysis. This is among the first observations of similar active sites in 2 different enzyme families catalyzing a similar reaction in opposite directions. Although the size and overall protein fold of factor XI11 and the cysteine proteinases are quite different, the active site and the surrounding protein structure share structural features suggesting a common evolutionary lineage. Here we present a description of the residues in the active site and the structural evidence that the catalytic mechanism of the transglutaminases is similar to the reverse mechanism of the cysteine proteinases.

Vitamin A is clearly an important factor in spermatogenesis. Some of the new data on metabolism of retinoids in the testis has contributed to our understanding of the mechanism(s) involved in the action of vitamin A. It is probable that the requirement of the testis of vitamin A deficient rats for retinol but not retinoic acid involves access of the retinoids to various testicular compartments. Retinol may be required by germinal cells because of a requirement for esterification in order to be successfully transported by the Sertoli cells. Existing evidence suggests that both the Sertoli cells and the germinal cells have specific requirements for retinoids. In the vitamin A deficient rat there appears to be a developmental block at preleptotene spermatocyte and type Al spermatogonia stages. This block is removed by retinol and germinal cell development reinitiates in a synchronous manner. The synchronous testis model offers a number of advantages for the study of molecular events associated with the cycle of the seminiferous epithelium and the development of germinal cells as well as for investigations into the mechanism of action of the retinoids.