How to avoid wrapping when using xml serializer format - wcf

Question

I have developed WCF service using XmlSerializerFormat. When i test it in WCF Test client i get following response.
Response is wrapped under tag <AuthenticateUserResult>. But when service is consumed using client proxy I get response with out wrap. Can someone Please assist how can i avoid the response wrap or how can i get both responses match.
WCF Test client Response:
<AuthenticateUserResponse xmlns="http://tempuri.org/">
<AuthenticateUserResult>
<applicationStatus>Success</applicationStatus>
<authType version="3.0">
<authenticationType xmlns="http://aaaaaaaa.xyz">0</authenticationType>
</authType>
</AuthenticateUserResult>
</AuthenticateUserResponse>
Service Response from Client Proxy:
<AuthenticateUserResponse >
<applicationStatus xmlns="http://tempuri.org/">Success</applicationStatus>
<authType version="3.0" xmlns="http://tempuri.org/">
<authenticationType xmlns="http://aaaaaaaa.xyz">0</authenticationType>
</authType>
</AuthenticateUserResponse>
My sample application
Service contract:
[ServiceContract]
[XmlSerializerFormat]
public interface IService2
{
[OperationContract]
[XmlSerializerFormat]
AuthenticateUserResponse AuthenticateUser();
}
//[DataContract()]
public class AuthenticateUserResponse
{
[XmlElement("applicationStatus", IsNullable = false)]
public ApplicationStatusType ApplicationStatus
{
get;
set;
}
[XmlElement("authType")]
public AuthType AuthType
{
get;
set;
}
}
[XmlRoot(Namespace = "http://aaaaaaaa.xyz")]
public class AuthType
{
[XmlAttribute("version")]
public string Version;
[XmlElement("authenticationType")]
public int AuthenticationType
{
get;
set;
}
}
public enum ApplicationStatusType
{
Success = 0,
Failed = 0
}