NOVELTY - Composition comprises a variant Cel5a endoglucanase having a temperature at which half of the maximal protein activity remains (T50) that is higher than a T50 of wild type Cel5a endoglucanase and increased enzymatic activity relative to wild type Cel5a endoglucanase.    USE - The composition and methods are useful for hydrolyzing cellulose; for expressing variant Cel5a endoglucanase protein having increased thermostability compared to wild type Cel5a (all claimed); and for producing biofuels.    ADVANTAGE - The variant Cel5a endoglucanase has T50 that is higher than a T50 of wild type Cel5a endoglucanase, or increased thermostability, and increased enzymatic activity relative to wild type Cel5a endoglucanase (all claimed). It also has increased expression in host, relative to wild type Cel5a. The improved variant Cel5a endoglucanase may be used to hydrolyze more cellulose at a higher temperature for a more efficient and cost-effective production of biofuels as compared to wild type Cel5a.    DETAILED DESCRIPTION - Composition comprises a variant Cel5a endoglucanase having a temperature at which half of the maximal protein activity remains (T50) that is higher than a T50 of wild type Cel5a endoglucanase and increased enzymatic activity relative to wild type Cel5a endoglucanase; or composition comprises a variant Cel5a endoglucanase having T50 that is higher than a T50 of wild type Cel5a endoglucanase and increased enzymatic activity relative to wild type Cel5a endoglucanase, the variant Cel5a endoglucanase having a mutation selected from Glu53Asp; Thr57Asn; Ser79Pro; Thr80Glu; Val101Ile; Ser133Arg; Asn153Asp; Asn155Glu; Thr156Glu; Gly189Ser; Phe191Val; Thr233Val; Gly239Glu; Val265Thr; Asp271Tyr; Gly293Ala; Ser309Trp/Leu; Ser318Pro/Gln/Glu; Gly189Ala, Phe191Val, Gly239Asp, Ser242Ala, Val265Thr, Asp271Tyr, Ser318Pro/Glu, and Ser322Ala; Glu53Asp, Thr57Asn, Ser79Pro, Thr80Glu, Val101Ile, Ser133Arg, Asn155Glu, Gly189Ser, Gly239Glu, Asp271Tyr, Gly293Ala, Ser309Leu, and Ser318Pro; Glu53Asp, Thr57Asn, Ser79Pro, Thr80Glu, Val101Ile, Ser133Arg, Asn155Glu, Gly189Ser, Gly239Glu, Asp271Tyr, Gly293Ala, Ser309Trp, and Ser318Pro; Glu53Asp, Thr57Asn, Ser79Pro, Thr80Glu, Val101Ile, Ser133Arg, Asn155Glu, Gly189Ser, Gly239Glu, Asp271Tyr, Gly293Ala, Ser309Leu, and Ser318Glu; Glu53Asp, Thr57Asn, Ser79Pro, Thr80Glu, Val101Ile, Ser133Arg, Asn155Glu, Gly189Ser, Gly239Glu, Asp271Tyr, Gly293Ala, Ser309Trp, and Ser318Glu; and Glu53Asp, Thr57Asn, Ser79Pro, Thr80Glu, Val101Ile, Ser133Arg, Asn155Glu, Gly189Ser, Phe191Val, Thr233Val, Gly239Glu, Val265Thr, Asp271Tyr, Gly293Ala, Ser309Trp, and Ser318Pro; or composition comprises a variant Cel5a endoglucanase having T50 that is higher than a T50 of wild type Cel5a endoglucanase, the composition comprising a point mutation selected from Asp13Glu, Thr18Pro, Glu53Asp, Thr57Asn, Asn76Pro, Ser79Pro/Gln, Thr80Glu, Ile82Met, Val101Ile, Ser133Arg, Ser139Pro, Asn153Asp, Asn155Glu/Gln, Thr156Glu, Gly189Ser/Ala/Glu, Phe191Val, Lys219Gln/Ala, Thr233Val, Gly239Glu/Asn/Asp, Val265Thr, Asp271Tyr/Phe, Tyr278Phe, Gly293Ala, Ser309Trp/Phe/Leu, Ser318Pro/Gln/Glu, and its combination; or composition comprises a variant Cel5a endoglucanase having increased protein expression in a host organism compared to wild type Cel5a, the composition comprising a point mutation selected from Asp13Glu, Thr18Pro, Gly64Ala, Asn76Pro, Ser79Pro/Gln/Glu, Thr80Glu/Gln, Ile82Leu/Met, Val101Ile/Leu, Ala122Glu, Ser133Arg, Ser139Pro, Asn155Glu/Gln, Thr156Glu, Gly189Ser/Ala/Glu/Lys, Lys219Gln/Ala, Gly239Glu/Asn/Asp, Val265Thr, Asp271Tyr/Phe, Tyr278Phe, Gly293Ala, Ser309Trp/Phe/Leu, and Ser318Pro/Gln/Glu; or composition comprises a variant Cel5a endoglucanase having a T50 above the T50 of wild type Cel5a endoglucanase, increased enzymatic activity relative to wild type Cel5a endoglucanase, and increased protein expression in a host organism relative to wild type Cel5a, the variant Cel5a endoglucanase having a combination of mutations selected from Gly189Ala, Pro191Val, Gly239Asp, Ser242Ala, Val265Thr, Asp271Tyr, Ser318Pro/Glu, and Ser322Ala; Glu53Asp, Thr57Asn, Ser79Pro, Thr80Glu, Val101Ile, Ser133Arg, Asn155Glu, Gly189Ser, Gly239Glu, Asp271Tyr, Gly293Ala, Ser309Leu, and Ser318Pro; Glu53Asp, Thr57Asn, Ser79Pro, Thr80Glu, Val101Ile, Ser133Arg, Asn155Glu, Gly189Ser, Gly239Glu, Asp271Tyr, Gly293Ala, Ser309Trp, and Ser318Pro; Glu53Asp, Thr57Asn, Ser79Pro, Thr80Glu, Val101Ile, Ser133Arg, Asn155Glu, Gly189Ser, Gly239Glu, Asp271Tyr, Gly293Ala, Ser309Leu, and Ser318Glu; Glu53Asp, Thr57Asn, Ser79Pro, Thr80Glu, Val101Ile, Ser133Arg, Asn155Glu, Gly189Ser, Gly239Glu, Asp271Tyr, Gly293Ala, Ser309Trp, and Ser318Glu; and Glu53Asp, Thr57Asn, Ser79Pro, Thr80Glu, Val101Ile, Ser133Arg, Asn155Glu, Gly189Ser, Phe191Val, Thr233Val, Gly239Glu, Val265Thr, Asp271Tyr, Gly293Ala, Ser309Trp, and Ser318Pro. INDEPENDENT CLAIMS are:    (1) a method of hydrolyzing cellulose, comprising hydrolyzing the cellulose with the composition; and    (2) a method of expressing a variant Cel5a endoglucanase protein having increased thermostability compared to wild type Cel5a, comprising expressing the composition in a host organism.