Abstract:
Variants with increased acyl transferase activity can be designed on the basis of a three-dimensional model by making amino acid alterations near the active Ser of lipolytic enzymes such as  C. antarctica  lipase A or the lipase/acyl transferase from  C. parapsilosis.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a polypeptide with lipolytic enzyme activity and to a method of preparing it. 
       BACKGROUND OF THE INVENTION 
       [0002]    WO2004064537 discloses a method for the in-situ production of an emulsifier in a foodstuff, wherein a lipid acyl transferase is added to the foodstuff. WO2005066347 discloses a method of producing a variant glycolipid acyl transferase enzyme. 
         [0003]    V Neugnot et al., European Journal of Biochemistry, Vol. 269 (6) pp. 1734-1745 (2002) March, describes a lipase/acyl transferase from  Candida parapsilosis.    
         [0004]    WO8802775A1 describes  Candida antarctica  lipase A. WO9401541A1 discloses variants of  C. antarctica  lipase A. 
       SUMMARY OF THE INVENTION 
       [0005]    The inventors have found that variants with increased acyl transferase activity can be designed on the basis of a three-dimensional model by making amino acid alterations near the active Ser of lipolytic enzymes such as  C. antarctica  lipase A or the lipase/acyl transferase from  C. parapsilosis.    
         [0006]    Accordingly, the invention provides a method of preparing a polypeptide, comprising:
   a) providing a three dimensional model of a parent polypeptide having lipolytic enzyme activity and an amino acid sequence with an active Ser having at least 80% identity to any of SEQ ID NOS: 1-5,   b) selecting an amino acid residue in the parent polypeptide which has a non-hydrogen atom within 10 Å of the a non-hydrogen atom in the active Ser in the model,   c) providing an altered amino acid sequence which is at least 80% identical to any of SEQ ID NOS: 1-5, and wherein the difference from the parent polypeptide comprises substitution or deletion of the selected residue or insertion of at least one residue adjacent to the selected residue,   d) preparing an altered polypeptide having the altered amino acid sequence,   e) determining the acyl transferase activity of the altered polypeptide, and   f) selecting an altered polypeptide which has an increased acyl transferase activity compared to the parent polypeptide.   
 
         [0013]    The invention also provides a polypeptide which: 
         [0014]    has lipolytic enzyme activity, and 
         [0015]    has an amino acid sequence which has at least 80% identity to SEQ ID NO: 1 and has a different residue at a position or has an insertion adjacent to a position corresponding to any of residues 82-87, 108, 132-133, 138, 140-142, 145, 172-179, 182, 202-216, 220-232, 235, 238, 241-242, 257,264, 267-268, 275-277, 280, 282-288, 290-296, 298-299, 304, 320, 324-328, 356-357, 360 and 420-421 of SEQ ID NO: 1. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  shows a three-dimensional model of  Candida antarctica  lipase A (CALA, SEQ ID NO: 1) with a substrate analog (myristic acid). 
           [0017]      FIG. 2  shows an alignment based on the three-dimensional structure of the following sequences in full-length or truncated form:
   SEQ ID NO: 1 (CAND_A)   SEQ ID NO: 5 (CaLIP1, ADY62089)   SEQ ID NO: 6 (ADY62090, CaLIP2)   SEQ ID NO: 7 (ABJ25493,  A. fumigatus  lipase)   SEQ ID NO: 2 ( Pseudozyma  lipase, ADZ72148)   SEQ ID NO: 4 (CpLIP2, Q8NIN8)   SEQ ID NO: 3 (CpLIP1, Q8NJ51)     
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Parent Polypeptide 
       [0025]    The invention uses a parent polypeptide with lipolytic enzyme activity. It may be  Candida antarctica  lipase A (CALA, SEQ ID NO: 1),  Pseudozyma  sp. lipase (SEQ ID NO: 2) described in WO2005040334,  C. parapsilosis  lipase CpLIP1 (SEQ ID NO: 3) or CpLIP2 (SEQ ID NO: 4), any of CaLIP1-10 from  Candida albicans , e.g. CaLIP1 or CaLIP2 shown as SEQ ID NOS: 5-6, or  Aspergillus fumigatus  lipase (SEQ ID NO: 7). 
       Three-Dimensional Model 
       [0026]    The invention uses a 3D model of the parent polypeptide.  FIG. 1  gives the coordinates for a 3D model of CALA with myristic acid as a substrate analogue. The active Ser is in position 174. 
       Selection of Amino Acid Residue 
       [0027]    An amino acid residue is selected in the 3D model having a non-hydrogen atom within 10 Å of a non-H atom of the active Ser. 
         [0028]    In the model in  FIG. 1 , the following residues have a non-H atom within 10 Å of a non-H atom of the active Ser (position 174 of SEQ ID NO: 1): 80-85, 108, 112, 116, 132-133, 139-140, 145, 171-182, 200-207, 211, 215, 220, 223, 264, 268, 318-321, 324-328, 332, 355-357, 359-361, 419-421, 425. 
       Altered Amino Acid Sequence 
       [0029]    The selected residue may be substituted with a different residue, particularly with a more efficient pi electron donor residue. Amino acid residues are ranked as follows from least efficient to most efficient pi donors (an equal sign indicates residues with practically indistinguishable efficiency). Other residues are not considered to be pi electron donors: 
         [0000]      T&lt;N&lt;H&lt;F&lt;Y&lt;W 
         [0030]    The substitution may particularly be conservative, i.e. substitution with another residue of the same type (negative, positive, hydrophobic or hydrophilic). The negative residues are D, E, the positive residues are K, R, the hydrophobic residues are A, C, F, G, I, L, M, P, V, W, Y, and the hydrophilic residues are H, N, Q, S, T. 
         [0031]    Alternatively, an amino acid insertion may be made at the N- or C-terminal side of the selected residue, particularly an insertion of 1-2 residues. 
         [0032]    CpLIP1 or CpLIP2 (SEQ ID NO: 3 or 4) may be used as a template for the amino acid alteration by referring to an alignment as shown in  FIG. 3  for SEQ ID NOS: 1-5. Thus, the selected residue may be substituted with the residue found in the corresponding position for SEQ ID NO: 3 or 4. The selected residue may be deleted if SEQ ID NO: 3 or 4 has a gap at that position. An insertion may be made adjacent to the selected residue if SEQ ID NO: 3 or 4 has an additional residue at that position; the insertion may in particular be the same residue found in SEQ ID NO: 3 or 4. 
       Particular Substitutions 
       [0033]    The variant may particularly comprise one or more of the following substitutions: Y83W, V103T and/or H132Y. More particularly, it may comprise the combination F223A F421V Y83W. 
       Nomenclature for Amino Acid Alterations 
       [0034]    In this specification, an amino acid substitution is described by use of one-letter codes, e.g. P205W. Multiple substitutions are concatenated, e.g. P205F T211W to indicate a variant with two substitutions. P205W, Y, F is used to indicate alternatives, i.e. substitution of P205 with W, Y or F. 
       Assay for Acyl Transferase Activity 
       [0035]    In general, the activity may be determined by incubating the polypeptide with an acyl ester as acyl donor and an alcohol as acyl acceptor in an aqueous system and analyzing the mixture after the incubation to determine the transfer of the acyl group. This may be done, e.g. as described in WO2004064537. 
       Use of Lipolytic Enzyme Variant 
       [0036]    The variants of the invention have increased acyl transferase activity. They may be used in various processes where they are mixed with an acyl donor and an acyl acceptor in an aqueous system to effect acyl transfer, e.g. as described in the indicated publications:
   In-situ production of an emulsifier in a foodstuff, such as baked goods made from dough, e.g. as described in WO2004064537.   Production of a carbohydrate ester, a protein ester or a hydroxyl acid ester, WO2004064987.   Reducing or removing diglyceride from edible oil, WO2005066351.   Enzymatic degumming of edible oil, WO2005066351.   
 
       Examples 
       [0041]