Account Teams can be used for Muliple Account Ownership in Private Sharing Model in Salesforce.

OWD Settings:

Enable Account Teams:

User from Line of Business 1:

a. Owner of Account.

b. Owner of One opportunity.

User from Line of Business 2:

a. Account Manager using Account Team. So, gets access to the Account.

b. Since Opportunity OWD is private, cannot see opportunities from other Line of Businesses.