c Thermostable alkaline pectate lyases have potential applications in the textile industry as an alternative to chemical-based ramie degumming processes. In particular, the alkaline pectate lyase from Bacillus sp. strain N16-5 (BspPelA) has potential for enzymatic ramie degumming because of its high specific activity under extremely alkaline conditions without the requirement for additional Ca 2؉ . However, BspPelA displays poor thermostability and is inactive after incubation at 50°C for only 30 min. Here, directed evolution was used to improve the thermostability of BspPelA for efficient and stable degumming. After two rounds of error-prone PCR and screening of >12,000 mutants, 10 mutants with improved thermostability were obtained. Sequence analysis and site-directed mutagenesis revealed that single E124I, T178A, and S271G substitutions were responsible for improving thermostability. Structural and molecular dynamic simulation analysis indicated that the formation of a hydrophobic cluster and new H-bond networks was the key factor contributing to the improvement in thermostability with these three substitutions. The most thermostable combined mutant, EAET, exhibited a 140-fold increase in the t 50 (time at which the enzyme loses 50% of its initial activity) value at 50°C, accompanied by an 84.3% decrease in activity compared with that of wild-type BspPelA, while the most advantageous combined mutant, EA, exhibited a 24-fold increase in the t 50 value at 50°C, with a 23.3% increase in activity. Ramie degumming with the EA mutant was more efficient than that with wild-type BspPelA. Collectively, our results suggest that the EA mutant, exhibiting remarkable improvements in thermostability and activity, has the potential for applications in ramie degumming in the textile industry. P ectin, a naturally ubiquitous constituent of the middle lamella of the primary cell wall in plants, is a heteropolysaccharide composed of ␣-1,4-linked galacturonate chains with a high percentage of methyl esterification and functions to form a network with other noncellulosic materials, such as proteins and waxes (1-3). Pectin degradation requires the combined action of several enzymes that can be classified into two main groups: methylesterases, which remove methoxyl groups from pectin, and depolymerases (hydrolases and lyases), which cleave the bonds between galacturonate units (4-6).Pectate lyases (Pels) (EC 4.2.2.2) cleave ␣-1,4-linked galacturonate units of pectate by -elimination, giving rise to an unsaturated C-4 -C-5 bond at the nonreducing end of the newly formed oligogalacturonate (7). Pels are widely distributed among microbial plant pathogens and have been the focus of several studies aiming to elucidate the roles of these enzymes as virulence factors (8, 9). Pels have also been found in some other microorganisms, including bacteria of the genus Bacillus (10) and some thermophilic bacteria (11). In general, Pels work efficiently at alkaline pH (between pH 8 and 10), and additional Ca 2ϩ ions are required for efficient enz...