g Cutinases have shown potential for hydrolysis of the recalcitrant synthetic polymer polyethylene terephthalate (PET). We have shown previously that the rate of this hydrolysis can be enhanced by the addition of hydrophobins, small fungal proteins that can alter the physicochemical properties of surfaces. Here we have investigated whether the PET-hydrolyzing activity of a bacterial cutinase from Thermobifida cellulosilytica (Thc_Cut1) would be further enhanced by fusion to one of three Trichoderma hydrophobins, i.e., the class II hydrophobins HFB4 and HFB7 and the pseudo-class I hydrophobin HFB9b. The fusion enzymes exhibited decreased k cat values on soluble substrates (p-nitrophenyl acetate and p-nitrophenyl butyrate) and strongly decreased the hydrophilicity of glass but caused only small changes in the hydrophobicity of PET. When the enzyme was fused to HFB4 or HFB7, the hydrolysis of PET was enhanced >16-fold over the level with the free enzyme, while a mixture of the enzyme and the hydrophobins led only to a 4-fold increase at most. Fusion with the non-class II hydrophobin HFB9b did not increase the rate of hydrolysis over that of the enzyme-hydrophobin mixture, but HFB9b performed best when PET was preincubated with the hydrophobins before enzyme treatment. The pattern of hydrolysis by the fusion enzymes differed from that of Thc_Cut1 as the concentration of the product mono(2-hydroxyethyl) terephthalate relative to that of the main product, terephthalic acid, increased. Small-angle X-ray scattering (SAXS) analysis revealed an increased scattering contrast of the fusion proteins over that of the free proteins, suggesting a change in conformation or enhanced protein aggregation. Our data show that the level of hydrolysis of PET by cutinase can be significantly increased by fusion to hydrophobins. The data further suggest that this likely involves binding of the hydrophobins to the cutinase and changes in the conformation of its active center. P olyethylene terephthalate (PET) is the best-known and most widespread synthetic polyester in the world. It is used for foils and bottles as well as for fibers for the textile industry (1). Recycling of PET and modification of its properties for different applications by traditional procedures involve harsh chemical and physicochemical treatments (2, 3). Enzymatic modification, particularly by cutinases, has been recognized as a powerful alternative in the past decade (4, 5) and, besides offering new avenues for PET recycling, has the additional advantage of creating a modified PET with increased dyeing efficacy and improved binding to polyvinyl chloride without altering the polymer's bulk properties (4, 5).On the other hand, enzymatic hydrolysis of PET has the inherent disadvantage of occurring at a very low rate (5, 6). The reasons for this are not yet clearly understood. The access of the active center of the cutinase to the insoluble substrate is apparently one of the rate-limiting points, because enlarging the areas around the active sites of cutinases from Fus...

No abstract

No abstract

We report bcc-like crystal structures in 2-4 ML Fe films grown on fcc Cu(100) using scanning tunneling microscopy. The local bcc structure provides a straightforward explanation for their frequently reported outstanding magnetic properties, i.e., ferromagnetic ordering in all layers with a Curie temperature above 300 K. The non-pseudomorphic structure, which becomes pseudomorphic above 4 ML film thickness is unexpected in terms of conventional rules of thin film growth and stresses the importance of finite thickness effects in ferromagnetic ultrathin films.Both academic interest in novel nanomagnetic phenomena as well as their technological importance for magneto-electronics and high density magnetic storage devices make the study of ultrathin ferromagnetic films particularly worthwhile. These extremely thin films, typically less than 10 monolayers (ML) thick, exhibit significantly different magnetic properties in contrast to the bulk material, e.g., different magnetization directions, enhanced magnetic moments, and lower Curie temperatures. Fe films epitaxially grown on Cu(100) are distinguished by a particular complex behavior since they are variable both with respect to magnetic ordering (ferroor antiferromagnetic) and crystal structure (fcc or bcc). Although the epitaxial system Fe/Cu(100) is under intense scrutiny for more than a decade and its magnetic properties have been mapped very precisely, no conclusive overall picture of the relation between structure and magnetic states has emerged yet. Regarding the model for films deposited at room temperature presently discussed in the literature, there is clear evidence for an antiferromagnetic, pseudomorphic fcc phase between 5 and 10 ML film thickness. The character and origin of the ferromagnetic phase between 2 and 4 ML, however, remains unclear. Low energy electron diffraction (LEED) [1], surface extended X-ray absorption fine-structure (SEXAFS) [2], and medium energy ion scattering studies (MEIS) [3] indicate a distinct distortion of the fcc lattice in 2-4 ML films. This reconstruction, which is considered to comprise the entire film thickness [1], is accompanied by a substantial increase of the film volume (interlayer distance) by about 5% [1,4]. In the past, these results led to the notion of a second, ferromagnetic fcc-like phase with an expanded film volume, i.e., a face centered tetragonal (fct) phase. While ab-initio calculations of bulk Fe do support the possibility of a ferromagnetic fcc phase with expanded volume under substantial tensile strain [5], the respective calculations of ultrathin films on Cu(100) did not provide an unambiguous confirmation of the ferromagnetic fct model [6,7]. This is an important question since the hypothetical existence of a ferromagnetic fcc-like phase is relevant also for the solid state physics of Fe. The two-γ-state model introduced by Kaufman, Clougherty, and Weiss [8], assuming two fcc states of bulk Fe either ferro-or antiferromagnetic, is still under discussion.In this Letter, we resolve this issue by char...

No abstract