Small linkers

In the absence of suitable functionality for direct attachment a small linker sidearm can be introduced, which contain an appropriate functionality at the terminal position. 

These transformations indicated that the starch binding domain of Rhizopus sp. glucoamylase was located at the N-terminus, and attached to the catalytic domain by a small linker domain (Figure 7.10). This is in contrast with the A. niger glucoamy-lases that have an opposite structure, with the catalytic domain at the N-terminus and the starch binding domain at the C-terminus. 

A simple formylacetal (CH2) has also been used as a linker for oligosaccharide synthesis on MPEG. This small linker allows the hindered hydroxyls, such as the 4-hydroxy group of glucose, to be installed on the MPEG [60]. The formylacetal linker is stable under the acidic conditions mostly used for glycosylation, but it is readily cleaved by Lewis acids (TMSI or Ce(OTf)x) or trifluoroacetic acid. A simplified work-up and purification procedure was also reported by use of the solid acid catalyst. 

Figure 8-10. Overview of small linker molecules recently characterized to molecular resolution by in situ STM on Au(lll)-electrode surfaces in aqueous buffer under potential control. A Bare reconstructed Au(l 11 )-surface. B (2 3 xV3)R30°-4 butanethiol monolayer (hydrophobic). C (2 3 x 6)R30°-6 monolayer of mercaptopropionic acid (negatively charged).D (V3 x 4)R30°-2 monolayer of cysteamine (positively charged). E (3 3 x 6)R30°-6 monolayer of cysteine/cystine (zwitterionic). ...

Fig. 1. Domain structure of the Hsp70 and Hsp70-related protein families. Schematic representation of the ATPase domain ( 385 residues, dark gray), a small linker, and the substrate-binding domain, which is subdivided into the /3-sheet ( 150 residues, light gray) and the a-helical subdomains ( 100 residues, gradient). The white boxes in the HspllO and Hspl70 families represent insertions of unknown function.

Inteins have several signature motifs (Fig. 1 and Table I). Blocks A, B, F, and also known as Blocks Nl, N3, C2, and Cl, respectively, are present in all inteins. Block A begins with the first residue of the intein and Block B is usually 60-100 amino acids from the start of the intein. Block F closely precedes Block G, which includes the end of the intein and the first residue of the carboxy-extein. Blocks C, D, E, and H (also known as Blocks ENl-4 ) are sometimes present between Blocks B and F and include the signature motifs of one class of endonuclease, termed the dodecapeptide (DOD) or LAGLI-DADG family of homing endonucleases (see below). Mini-inteins (<200 aa) have a small linker in place of the homing endonuclease domain. 

Construction of High Nuclearity Lanthanide Complexes Using Small Linkers 291... 

CONSTRUCTION OF HIGH NUCLEARITY LANTHANIDE COMPLEXES USING SMALL LINKERS... 

A simple formylacetal (CH2) has also been used as a linker for oligosaccharide synthesis on MPEG. This small linker allows the hindered hydroxyls, such as 4-hydroxy... 

The physicochemical differences between proteins and membranes originate from their basic constituents. While proteins are composed of amino acids, membranes are made of lipids amphipathic molecules characterized by having a polar head at one extremity and a highly hydrophobic moiety at the other end, typically in the form of hydrocarbon chains, with the two ends usually connected by a small linker (most frequently glycerol or sphingosin). 

Small amounts of specially functionalized monomers are often copolymerized with acryUc monomers in order to modify or improve the properties of the polymer. These functional monomers can bring about improvements either directiy or by providing sites for further reaction with metal ions, cross-linkers, or other compounds and resins. Table 9 Hsts some of the more common functional monomers used in the preparation of acryUc copolymers. 

Linker-Scanning Mutagenesis. Using linker-scanning mutagenesis (24) small sequences of DNA are removed and replaced with a synthetic restriction fragment or linker. This technique is commonly used in analysis of promoters and other control sequences in DNA, while preserving the spatial relationship between the sequences. 

The apical domain (blue), which is a p sandwich flanked by a helices, is formed by the middle region of the polypeptide chain. The two linker regions between the equatorial and the apical domains form a small infermediate domain (purple) comprising three a helices. 

Histones are small, basic proteins required to condense DNA into chromatin. They have been first described and named in 1884 by Albrecht Kossel. There are five main histones HI, H2A, H2B, H3 andH4. An octamer of core histones H2A, H2B, H3 andH4 is located inside a nucleosome, the central building block of chromatin, with about 150 base pairs of DNA wrapped around. The basic nature of histones, mediated by the high content of lysine and arginine residues, allows a direct interaction with the acidic phosphate back bone of DNA. The fifth histone HI is located outside at the junction between nucleosomes and is referred to as the linker histone. Besides the main histones, so-called histone variants are known, which replace core histones in certain locations like centromers. 

Stress fibers are parallel bundles of actin filaments that develop in the cytoplasm of fibroblasts from the cortical actin network in response to mechanical tension. These often bind to the plasma membrane at focal contacts and, through transmembrane linker glycoproteins, to the extracellular matrix. Thus, actin filaments of stress fibers indirectly Join to the inner face of the plasma membrane through molecular assemblies of attachment proteins, which include an actin-capping protein, a-actinin, vinculin, and talin (Small, 1988). 

Krier M, de Araujo-Junior JX, Schmitt M, Duranton J, Justiano-Basaran H, Lugnier C, Bourguignon JJ, Rognan D. Design of small-sized libraries by combinatorial assembly of linkers and functional groups to a given scaffold application to the structure-based optimization of a phosphodiesterase 4 inhibitor. J Med Chem 2005 48 3816-22. 

Hyun et al. [345] prepared PbS Q-dots in a suspension and tethered them to Ti02 nanoparticles with a bifunctional thiol-carboxyl linker molecule. Strong size dependence due to quantum confinement was inferred from cyclic voltammetry measurements, for the electron affinity and ionization potential of the attached Q-dots. On the basis of the measured energy levels, the authors claimed that pho-toexcited electrons should transfer efficiently from PbS into T1O2 only for dot diameters below 4.3 nm. Continuous-wave fluorescence spectra and fluorescence transients of the PbS/Ti02 assembly were consistent with electron transfer from small Q-dots. The measured charge transfer time was surprisingly slow ( 100 ns). Implications of this fact for future photovoltaics were discussed, while initial results from as-fabricated sensitized solar cells were presented. 

An alternative to most of these mechanisms is the existence of efficient efflux systems, so that toxic concentrations of the drug are not achieved. There are three major families of proton-dependent multidrug efflux systems (1) the major facilitator superfamily, (2) the small multidrug resistance family, and (3) the resistance/nodulation/cell division family (Paulsen et al. 1996). It should be emphasized that several of these systems are involved not with antibiotic efflux but with, for example, acriflavine, chlorhexidine, and crystal violet. An attempt is made only to outline a few salient features of the resistance/nodulation/cell division family that mediates antibiotic efflux, and these are given in Table 3.3 (Nikaido 1996). They consist of a transporter, a linker, and an outer membrane channel. 

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