At the nonpermissive temperature, premature chromosome condensation (PCC) occurs in tsBN2 cells derived from the BHK cell line, which can be converted to the Ts+ phenotype by the human RCC1 gene To prove that the RCC1 gene is the mutant gene in tsBN2 cells, which have RCC1 mRNA and protein of the same sizes as those of BHK cells, RCC1 cDNAs were isolated from BHK and tsBN2 cells and sequenced to search for mutations The hamster (BHK) RCC1 cDNA encodes a protein of 421 amino acids homologous to the human RCC1 protein In a comparison of the base sequences of BHK and BN2 RCC1 cDNAs, a single base change, cytosine to thymine (serine to phenylalanine), was found in the 256th codon of BN2 RCC1 cDNA The same transition was verified in the RCC1 genomic DNA by the polymerase chain reaction method BHK RCC1 cDNA, but not tsBN2 RCC1 cDNA, complemented the tsBN2 mutation, although both have the same amino acid sequence except for one amino acid at the 256th codon This amino acid change, serine to phenylalanine, was estimated to cause a profound structural change in the RCC1 protein

Premature chromosome condensation is induced by a point mutation in the hamster RCC1 gene.

/pdf/protein-structure-and-function-from-a-colloidal-to-a-1t1d4qfdqn.pdf

Protein structure and function, from a colloidal to a molecular view

Predicting Three‐Dimensional Structures of Oligopeptides

Although the peptide $Boc-{Aib}^1-{Ala}^2-{Leu}^3-{Aib}^4-{Ala}^5-{Leu}^6-{Aib}^7-{Ala}^8-{Leu}^9-{Aib}^{10}-OMe$ [with a t-butoxycarbonyl (Boc) blocking group at the amino terminus, a methyl ester (OMe) at the carboxyl terminus, and four \alpha-aminoisobutyric (Aib) residues] has a 3-fold repeat of residues, the helix formed by the peptide backbone is irregular. The carboxyl-terminal half assumes an \alpha-helical form with torsion angles \phi and \psi of approximately -60 deg and -45 deg, respectively, whereas the amino-terminal half is distorted by an insertion of a water molecule between the amide nitrogen of ${Ala}^5$ [N(5)] and the carbonyl oxygen of ${Ala}^2$ [O(2)]. The water molecule W(1) acts as a bridge by forming hydrogen bonds N(5)...W(1) (2.93 A) and W(1)...O(2) (2.86 A). The distortion of the helix exposes the carbonyl oxygens of ${Aib}^1$ and ${Aib}^4$ to the outside environment, with the consequence that the helix assumes an amphiphilic character despite having all apolar residues. Neighboring helices in the crystal run in antiparallel directions. On one side of a helix there are only hydrophobic contacts with efficient interdigitation of leucine side chains with those from the neighboring helix. On the other side of the helix there are hydrogen bonds between protruding carbonyl oxygens and four water molecules that separate two neighboring helices. Along the helix axis the helices bind head-to-tail with a direct hydrogen bond N(2)...O(9) (3.00 A). Crystals grown from methanol/water solution are in space group ${P2}_1$ with a = 15.778 \pm 0.004 A, b = 11.228 \pm 0.002 A, c = 18.415 \pm 0.003 A, \beta = 102.10 \pm 0.02 deg, and two formula units per cell for $C_{49}H_{88}N_{10}O_{13}. {2H}_2O.{CH}_3OH$. The overall agreement factor R is 7.5% for 3394 reflections observed with intensities >3\sigma(F), and the resolution is 0.90 A.

https://www.pnas.org/content/pnas/85/2/299.full.pdf

Aqueous channels within apolar peptide aggregates: solvated helix of the alpha-aminoisobutyric acid (Aib)-containing peptide Boc-(Aib-Ala-Leu)3-Aib-OMe.2H2O.CH3OH in crystals.

A method is developed to extract the entropy of polypeptides and proteins from samples of conformations. It is based on techniques suggested previously by Meirovitch, and has the advantage that it can be applied not only to states in which the molecule undergoes harmonic or quasiharmonic conformational fluctuations, but also to the random coil, as well as to mixtures of these extreme states. In order to confine the search to a region of conformational space corresponding to a stable state, the transition probabilities are determined not by “looking to the future,” as in the previous method [H. Meirovitch and H. A. Scheraga (1986) J. Chem. Phys.84, 6369–6375], but by analyzing the previous steps in the generation of the chain. The method is applied to a model of decaglycine with rigid geometry, using the potential energy function ECEPP (Empirical Conformational Energy Program for Peptides). The model is simulated with the Metropolis Monte Carlo method to generate samples of conformations in the α-helical and hairpin regions, respectively, at T = 100 K. For the α-helix, the four dihedral angles of the N- and C-terminal residues are found to undergo full rotational variation. The results show that the α-helix is a more stable structure than the hairpin. Both its Helmholtz free energy F and energy E are lower than those of the hairpin by ΔF ∼ 0.4 and ΔE ∼ 0.3 kcal/mole/residue, respectively. It should be noted that the contribution of the entropy ΔS to ΔF is significant (TΔS ∼ 0.1 kcal/mole/residue). Also, the entropy of the α-helix is found to be larger than that of the hairpin. This is a result of the extra entropy arising from the rotational freedom about the four terminal single bonds of the α-helix.

Stability of polypeptide conformational states as determined by computer simulation of the free energy.

Even though poly(L-valine) and poly(L-isoleucine) both contain residues that are branched at their β-carbon atoms, they exhibit a different behavior of their Zimm-Bragg helix-growth parameter s in aqueous solution. This quantity increases with temperature for poly(L-valine) but decreases for poly(L-isoleucine). The origin of this behavioral difference was examined by computing theoretical values of s versus temperature from interatomic interaction energies, taking solvent (hydrophobic and hydrophilic) effects into account. The calculated s versus temperature curves for both homopolymers are consistent with the observed experimental behavior. The two homopolymers behave differently because of differences in the change in the number of hydration-shell water molecules accompanying their helix–coil transitions. The larger isoleucine side chains are more crowded together in both the α-helical and coil forms than are those of valine. Therefore, there is a smaller change in hydration of the isoleucine side chains compared to that of the valine side chains in the helix–coil transition. By analyzing the effects of hydration on the s versus temperature curves, it is possible to account also for the experimental curve for poly(L-leucine), which exhibits an intermediate behavior between those for poly(L-valine) and poly(L-isoleucine).

Molecular theory of the helix-coil transition in polyamino acids. V. Explanation of the different conformational behavior of valine, isoleucine, and leucine in aqueous solution

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Molecular theory of the helix-coil transition in polyamino acids. V. Explanation of the different conformational behavior of valine, isoleucine, and leucine in aqueous solution