Holo-proteins

The reaction of the holo-protein with AuSTm occurs in two phases with each step showing first-order dependence on the MT concentration but independent of AuSTm [105] ... 

The rates are essentially independent of the distribution of metal in the MT with similar rates between Zn7—MTm (Cd, Zn)7-MT, and Cd7—MT. The values of the rate constants are ks = 6.9( 0.9) x 10 " s and kf=2.7( 1.2) x 10 s for the holo-protein. The slow rate constant is similar in magnitude to the first-order protein-dependent steps observed for reactions of DTNB (5,5 -dithiobis(2-nitrobenzoate)), EDTA (ethylenediamine tetraacetate), cisplatin, and other reagents, which has been attributed to a rearrangement of the protein. The fast step is more rapid by an order of magnitude, which suggests that other mechanisms are prevailing. 

Moliaka, Y.K., Grigorenko, A., Madera, D., Rogaev, E.I. (2004) Impas 1 possesses endopro-teolytic activity against multipass membrane protein substrate cleaving the presenUin 1 holo-protein. FEBS Lett., 557, 185-192. 

Thioneins are apoproteins that are exceptionally sulfur-rich (composed of greater 30 mol% cysteine). These proteins are found in high abundance in liver and kidney cytoplasm where they form metallothioneins (the holo-protein forms) upon complexation with metal ions. Thi-onein synthesis is induced by the presence of metals, especially zinc, copper, mercury, and cadmium. 

To compare apo- and holo-forms of proteins after both structures have been determined independently, crystallographers often compute difference Fourier syntheses (Chapter 7, Section IV.B), in which each Fourier term contains the structure-factor difference FAc>/c(-—F 0. A contour map of this Fourier series is called a difference map, and it shows only the differences between the holo-and apo- forms. Like the FQ — Fc map, the FAoio—F map contains both positive and negative density. Positive density occurs where the electron density of the holo-form is greater than that of the apo-form, so the ligand shows up clearly in positive density. In addition, conformational differences between holo- and apo-forms result in positive density where holo-protein atoms occupy regions that are unoccupied in the apo-form, and negative... 

Any one cone cell contains only one type of opsin and is sensitive to only one color of light. Color blindness results from loss or mutation of one or the other of the cone opsins. The combination of 11-c/s-retinaldehyde with cone opsin is sometimes called iodopsin, with rhodopsin meaning more specifically the holo-protein of rod opsin. Most studies of the mechanisms of vision shown in Figure 2.5 have been performed using rods by extrapolation, it is assumed that the same mechanisms are involved in cone vision. 

One of the first metalloregulatory proteins to be characterized extensively is the prokaryotic MerR transcription factor (1, 6, 7), which acts either as a repressor (apo-protein) or an activator (holo-protein) of the mer operon encoding mercury resistance proteins (Fig. Ic). The —35 and —10 sequence elements of the mer promoter, binding sites for the RNA polymerase initiation complex, are separated by an unusually long distance that results in poor constitutive transcription. Apo-MerR binds to the DNA between these sequences and bends the DNA, which results in a slight increase in repression on the suboptimal promoter. It also recruits the RNA polymerase to the transcription start site where it waits in a stalled complex. Upon binding of... 

The crystal structure of CRBPll is closest to that of CRBP. The Ca positions agree within 0.7 A, as is apparent in Table II. Unlike bound retinol in CRBP, the dihedral angle between the plane of the jS-ionone ring and the chain is not an ideal cis or trans (Winter et al., 1993). In the report of the crystal structure, the complementarity between the bound retinol and protein was examined and appeared fairly good (Winter a/., 1993). In the holo protein, within the cavity there are five empty spaces that are not occupied by retinol atoms. Most of these subcavities contain water molecules, which appear to be an integral part of the protein structure because they occupy similar positions in the apo structure. 

Apo and holo-protein Apo-protein denotes the amount of protein not saturated with its ligand (e.g. cobalamin) while holo-protein denotes the part of the protein saturated with its ligand. 

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