Cooperativity of the Coil-Globule Transition in a Homopolymer: Microcalorimetric Study of Poly(N-isopropylacrylamide)

Tiktopulo, E. I.; Bychkova, Valentina E.; Rička, J.; Ptitsyn, Oleg B.

doi:10.1021/ma00088a031

Cited by 227 publications

(236 citation statements)

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“…It is not the sharpness of a cooperative transition that distinguishes one-state from two-state behavior, but the number of identifiable populations. Very sharp one-state homopolymer collapse transitions (1-2 "C widths) are observed in PNIPAM (Tiktopulo et al, 1994;see Fig. 3).…”

mentioning

confidence: 87%

“…Homopolymers are predicted to collapse when they are put into "poor" solvents (i.e., solvents that prefer phase separation to mixing with monomers of the type that comprise the homopolymer) (Anufrieva et al, 1968;Ptitsyn et al, 1968;de Gennes, 1975;Post & Zimm, 1979;Sanchez, 1979;Williams et al, 1981). It is observed experimentally that polystyrene, a chain of nonpolar monomers, collapses to a compact globule in a poor organic solvent (Sun et al, 1980) and poly-(Nisopropylacrylamide) (PNIPAM) collapses very sharply (with increasing temperature) in water (Fujishige et al, 1989;RiEka et al, 1990;Meewes et al, 1991;Tiktopulo et al, 1994), resembling the renaturation of cold-denatured proteins (Privalov & Gill, 1988;see Fig. 3).…”

Section: Nonlocal Interactions Drive Collapse Transitions Whereas Lomentioning

confidence: 99%

“…This has been a matter of contention (Ptitsyn et al, 1968;de Gennes, 1975;Post & Zimm, 1979;Sanchez, 1979;Grosberg & Khokhlov, 1987). Although Ptitsyn et al (1968) argued that homopolymer collapse should be two-state in the limit of infinite chain length, it now appears that the collapse of a flexible homopolymer chain of finite length is a onestate transition (Sun et al, 1980;Tiktopulo et al, 1994), unless chain stiffness is high, as in DNA (de Gennes, 1975;Post & Zimm, 1979;reviewed by Chan & Dill, 1991a. In this regard the collapse of flexible homopolymers is less cooperative than the two-state folding attributed to small globular proteins.…”

Section: Protein Folding Cooperativity: a Simplest Hypothesismentioning

confidence: 99%

“…--~ also "freeze" upon collapse of PNIPAM homopolymers (Binkert et al, 1991), but this does not result in two-state behavior (Tiktopulo et al, 1994), indicating that side-chain freedom is not the origin of two-state behavior, at least in PNIPAM. Second, small-angle X-ray scattering experiments described below indicate much broader conformational diversity of backbones in compact denatured states than is expected from the native-like backbones of the side-chain molten globule model (summarized in Lattman et al, 1994).…”

Section: Protein Folding Cooperativity: a Simplest Hypothesismentioning

confidence: 99%

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Principles of protein folding — A perspective from simple exact models

et al. 1995

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General principles of protein structure, stability, and folding kinetics have recently been explored in computer simulations of simple exact lattice models. These models represent protein chains at a rudimentary level, but they involve few parameters, approximations, or implicit biases, and they allow complete explorations of conformational and sequence spaces. Such simulations have resulted in testable predictions that are sometimes unanticipated: The folding code is mainly binary and delocalized throughout the amino acid sequence. The secondary and tertiary structures of a protein are specified mainly by the sequence of polar and nonpolar monomers. More specific interactions may refine the structure, rather than dominate the folding code. Simple exact models can account for the properties that characterize protein folding: two-state cooperativity, secondary and tertiary structures, and multistage folding kinetics-fast hydrophobic collapse followed by slower annealing. These studies suggest the possibility of creating "foldable" chain molecules other than proteins. The encoding of a unique compact chain conformation may not require amino acids; it may require only the ability to synthesize specific monomer sequences in which at least one monomer type is solvent-averse.Keywords: chain collapse; hydrophobic interactions; lattice models; protein conformations; protein folding; protein stabilityWe review the principles of protein structure, stability, and folding kinetics from the perspective of simple exact models. We focus on the "folding code''-how the tertiary structure and folding pathway of a protein are encoded in its amino acid sequence. Although native proteins are specific, compact, and often remarkably symmetrical structures, ordinary synthetic polymers in solution, glasses, or melts adopt large ensembles of more expanded conformations, with little intrachain organization. With simple exact models, we ask what are the fundamental causes of the differences between proteins and other polymers-What makes proteins special?One view of protein folding assumes that the "local" interactions among the near neighbors in the amino acid sequence, the interactions that form helices and turns, are the main determinants of protein structure. This assumption implies that isolated helices form early in the protein folding pathway and then assemble into the native tertiary structure (see Fig. 1). It is the premise behind the paradigm, primary + secondary -+ tertiary structure, that seeks computer algorithms to predict secondary structures from the sequence, and then to assemble them into the tertiary native structure.Here we review a simple model of an alternative view, its basis in experimental results, and its implications. We show how the nonlocal interactions that drive collapse processes in heteropolymers can give rise to protein structure, stability, and folding kinetics. This perspective is based on evidence that the folding code is not predominantly localized in short windows of the amino acid sequence. It...

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mentioning

confidence: 87%

Section: Nonlocal Interactions Drive Collapse Transitions Whereas Lomentioning

confidence: 99%

Section: Protein Folding Cooperativity: a Simplest Hypothesismentioning

confidence: 99%

Section: Protein Folding Cooperativity: a Simplest Hypothesismentioning

confidence: 99%

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Principles of protein folding — A perspective from simple exact models

et al. 1995

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“…In his seminal work, de Gennes 7,8 built upon the approach of Flory 9 to describe the CGT as the transition of a tricritical magnetic system, inferring that it had to be a continuous transition. Although a large number of experiments have confirmed such prediction, there has also been evidence for discontinuous transitions [10][11][12] , findings that have been to date difficult to reconcile with the theory. Moreover, and more fundamentally from a conceptual point of view, proteins are known to undergo in most cases a two-state kind of transitions, where the folded (native in the biochemistry language) and the unfolded states coexist at the transition.…”

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confidence: 99%

First-order coil-globule transition driven by vibrational entropy

et al. 2012

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By shifting the balance between conformational entropy and internal energy, polymers modify their shape under external stimuli, such as changes in temperature. Prominent among such transformations is the coil-globule transition, whereby a polymer can switch from an entropydominated coil conformation to a globular one, governed by energy. The nature of the coilglobule transition has remained elusive, with evidence for both continuous and discontinuous transitions, with the two-state behaviour of proteins as an instance of the latter. Theoretical models mostly predict second-order transitions. Here we introduce a model that takes into consideration hitherto neglected features common to any polymer. We show that a firstorder phase transition smoothly appears as a function of the model parameters. our results can relieve part of the conflicts between theory and experiments in the field of protein folding, in the wake of recent studies tracing back the remarkable properties of proteins to basic polymer physics.

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